Before you get to the real post.... This got long. Please don't take this as me being "that" concerned about what accessories you get for your lathe. This is my thoughts on WHY i have the opinion that I do, and how I got to them. I find choices likes the one you posed to come up over and over again for me. Either the "what can I afford" question, or the "what do I want to afford" question.
99% of the lathes I seen in Taiwan all use 4 way toolpost.
Let me toss out something, Point of view. Attitude maybe. Possibly bordering philosophy about owning and using tools. Any tool, no matter how good, or how poor, is more than capable of doing something. Any tool, no matter how good or how poor, is more then capable of doing good work, within it's limits. Any tool, no matter how good or how poor, is more than capable of doing bad work, or no work at all when it's outside of it's limits. It's up to the end user to know how to use the tool well, to know the tools limits, to know how to finess just a little bit more out of the tool, to operate the tool quickly and efficiently, and to learn to plan and execute work in a way that the tool will show it's best side, and not it's worst. All of that takes practice. It doesn't matter what tool post you have, you're gonna have to get familiar with it, and comfortable with it before you're going to be proficient with it. And you're gonna have to go through some disappointment before you learn how to get it to work for you the way you'd like it to.
Now, you say that 99% of lathes in Taiwan all use a four way post? What does that say about the dovetail type tool post that you're considering? Given their very low cost, and very high availability, given that their availibility comes from at least 6 nations that I have stumbled across... IF there was a high demand for them... Somebody would be bringing them in, and your dilema would be solved, and you could have whatever tool holder you wanted, in whatever color you wanted, in no time flat.
What your statement says to me, is that 99.9 percent of lathe operators in Taiwan have come to be familiar with the operation and use of the four way tool post, and have not found it worth changing to a different style. If I was in your shoes looking at your four way tool post, wondering what am I going to do from here.... (Again, my attitude and philosophy here, when you start draging home commercial machine tools just for sport.... Normal logic might just not apply any more.) Personally, I wouldn't be blaming the tool post for being in my way or slowing me up. I wouldn't be blaming the lathe. I would be questioning myself, and what is it that I am not seeing, yet all of the lathe operators around me ARE seeing? What am I not doing that the lathe operators around me ARE doing. It's quite obvious, by your estimate of how many lathes you see with that four way tool post, and by my observation of how many local job shops here choose a four way tool post. (Here, where "the internet" portrays us ALL as using one of two styles of quick change tool posts....). I do visit a couple of such shops, several hydraulic shops, job shops, a fabrication shop. You will find a couple of dovetail style quick change tool posts. You'll also find that nobody in the same shop found it necessary to upgrade a second lathe to that. Here, in "the real world", where commercial work is being done on manual machines, they ARE out there, but they're just not that popular. Probably a lot more popular in a production shop, than a "one off" type of shop, but still. Four way tool posts are not "unpopular" at all. That means that have to work pretty well.
So in the end, it's your lathe, so regardless of functionality, you should have ANY toolpost that YOU LIKE installed on it, eventually. For now though, going with your statement of budget constraints. Don't look at your existing tool post as a hinderance, or even an inconvenience. It's just another tool that you have to learn to use. I promise you that when you do get the dovetail quick change tool post (now or in the future), you're just gonna have another learning curve, learning to make it work for you. You WILL enjoy it, once you're familiar with it. And in the end it will work for you. I've got nothing bad to say about them. I don't choose to use one, (although I have not ruled one out either, but it's not on the short list.) My opinion is NOT because they don't work. They do. But they are not the magical thing you see on the internet. Not because the tool post is or is not magic. (They are not magic). But because it's just another tool. It will work for you because you will learn to make work for you, and it will ALWAYS need more improvement, in the form of new holders, to keep you from having to take out and reset every tool that you use anyway, just like you're doing right now. All of this means that I don't believe that you are going to see the immediate gratification that you are looking for. It'll be more like the beginning of a journey. Every new cutter is gonna need a new holder. Which in turn is going to need a new quick change holder to attach to the tool post. Which drags out the tool budget over a VERY long span of time, to get to where you ware happy. Because cutting tools are things you NEED if you're going to cut things, the quick change post (Especially early on) just leads to making the essential tooling more expensive. You can and will get there, where you have everything you'll need, but like most things "more modern", each new thing you do means more stuff to buy. The four way post? One new tool, and a few minutes to cut some more shims out of the sheet of whatever metal you came up with to make shims out of, and that's that.
Buying a 3 jaw scroll chuck on the other hand- That WILL give you an immediate gratification, right off the bat, because it's easy. It WILL give you an IMMEDIATE time savings, as whatever you clamp in there is as centered as it's gonna get. You've only got to check that it is straight in the jaws. It WILL give you an IMMEDIATE reward on your investment. And not the least of it's benefits is that it's one purchase and it's done. There's nothing more you'll "need" to go with it. There's nothing more you'll "need" to gain the functionality that you would expect from a 3 jaw scroll chuck.
So now that I've applied my tool philosiphy in general to your situation, and that's out of the way..... A more practical reason perhaps.
Suppose I have enough budget to buy a QTCP with one or two holders, or a 3 jaw chuck with bolt on jaws (both cost me the same), which should I get first? Right now I only have a 4 jaw chuck.
If you bought a dovetail style quick change tool post with one or two holders, that leaves you two tool positions short of where you already are. You have a new holder, at what sounds like (relatively speaking) a significant cost. You're still having to swap tooling into and out of the quick change holders, dial them on center, all of that stuff. Yes, you can "dial" it in that way, and not shim, but as I said, shimming does not need to be "worked out" every time. Keep the shims with the tool. So once and done. That sounds like an expensive step backwards to live with one more extra "link in the chain" between your top slide and the spinning work. And of course more tool holders are not "that" expensive. (Way more than shims though). So when you're (still) frustrated about changing tools back and forth, and having to set them up again and again, you're gonna get another holder. And another. And another. And another......
And, in exchange for that temporary step backwards, you're still clocking in EVERYTHING you turn on a four jaw chuck? How convenient is that? How much time does that take, relative to setting a tool's height? You really (almost) need a four jaw chuck. As you become comfortable with what it will do (AND it's limitations), that can do magic for you. They're amazing. But they burn up time and thought when setting up some of the weird stuff that you'll come across. So while you'll never want to be without it, I'd bet that the absolute vast majority of your work could be tossed into 3 jaw scroll chuck. With little thought and a little planning, lmost as much work could be tossed into an under priced, under spec'ed, non quality controlled 3 jaw scroll chuck with heaps of runout in it. You do have a four jaw chuck already after all, so you do have a bailout for the times it doesn't work out.
In the end, that's my opinion. From two very distinct directions, I think you should postpone any changes to the tool post, and consider the scroll chuck to be a higher priority.
Now that I've said all of that, I have another thought. The suggestions here in this thread, about build a Norman style tool post, along with some very inspiring pictures- I don't know if that definitely idea is for you or not, but I would highly recommend that you consider it. I did this originally to support a parting tool, which proved difficult for me in the lantern tool post. Turns out, it's difficult either way, and as I built my skills get better with that, it makes less and less difference which method I use to present the tool. I also made holders to support a couple of tools that I am not equipped to hold in the lantern post. It is a few bucks up for some steel, but it's cheap steel (as steel goes), and it'll come in sizes that makes multiples, so there are spares if you scrap a part. The whole project can be done 100 percent, start to finish, right on the lathe if you have a drill chuck for the tailstock, and you are equipped to part the work with a parting tool. Or you could (I'd hate to, but you could..) cut the work with a hack saw and be just fine. The drilling could, without much difficulty, be done with a hand held drill. It's also low consequence, in that there is some tolerance. If you hand drill your holes a little crooked, it'll still work fine. If you hack saw a cut a little crooked, you can face it in the lathe and pretty it up. Or you can leave it as it is, it'll work fine. If you miss a bore by a couple thousandths, it might not lock as crisply as you'd like, but it WILL still lock solid. Heck, even if you bored the main hole a little crooked... I don't even know how that would be possible to do, but if you did... You're going to use that bore to mount the holder to mill the slot, so It's self correcting.. The tool will automatically be presented level. If it's a little ugly... It's fully functional to machine the next one. No step is inherently difficult to learn (except maybe parting, if you end up separating metal that way, but you don't have to by any means). It's a beautiful project though because there are a LOT of steps, a LOT of uncommon setups, and you will practice a LOT of ways to leverage your lathe, and your four way tool post to do a lot of things on a lathe that most people wouldn't even consider that a lathe could have done. It is not the kind of project that's going to win you a prize, although a couple on this site have come close to that mark, but it is more like the kind of project that builds prize winning skills, and whether the end result is show piece quality, or just kind of ugly, it's still fully functional, useful, and enjoyable. I know this because my tool holder with the crooked bore and the locking bolt on the wrong side works EVERY BIT AS GOOD as the ones I settled down and paid attention to, which came out much nicer cosmetically. Food for thought if you're looking for a functional, useful excuse to become more familiar with the tools you have at hand. In this, and anywhere you use tools, there is a certain satisfaction in turning out good work from raw materials. And even more satisfaction in doing it with tools that you've made yourself from raw materials.
