I agree with Mikey, I'd buy better quality collets. I use Techniks ER collets & they are the best bang for the buck. I use ER-40 & ER-16 for tool holding for the mill.
ER collets weren't designed for workholding even though many people do use it for that. ER collets aren't good for holding short workpieces, it's best to have at least 2/3, full length is best, of the workpiece engaged in the collet. This why 5C is better for work holding but ER collets have a wider clamping range so less collets are needed compared to 5C. ER collets for work holding is slow to use also.
Like everyone else I made me a ER collet chuck for the lathe. Because of this plan I went with ER-40 for the mill so I could use the same collets for the lathe to save money. Well between my 6-jaw & 3-jaw Set-Tru chucks as well as my 4-jaw I never use the ER collet chuck. My 6-jaw is pretty much like a collet chuck except a collet chuck is much safer for your knuckles working up close. I regret going with ER-40. I wish I had gone with ER-32 for the mill & never made the ER-40 chuck for the lathe.
Since I use ER for tool holding, I don't have a need for a full set of collets. The smallest I run in the ER-40 is 1/2" end mills, maybe 3/8". 3/8" and smaller for the mill I use ER-16. ER-40 just gets in the way for holding small end mills, like a 1/8" end mill in an ER-40 chuck is just ridiculous. I use nominal sizes for endmills so I only need a number of sizes for each chuck, even if I added metric size endmills to my arsenal I still wouldn't need a full set of collets. Would just be a waste of money for me.