I bought a longevity plasma cutter last year.. I'm just a hobby user, i've used it about 6 times, i've had no problems with it, although I feel it is underpowered.. I'm usually working on automotive type stuff and 1/4" is usually the max thickness material I mess with, and it does fine, but I think anything over 3/8 would give it problems..
I bought mine as a step up from the chinese units sold on ebay, the warranty helped... I didnt have much money in the longevity unit as I sold another older bluepoint plasma cutter and made a very good profit from the sale, I had about $200 invested in the Longevity plasma cutter..
If i were going to buy a plasma unit today I would buy a thermal dynamics cutmaster 42, it seems to be about the best bang for the buck...
Hypertherm plasma cutters are nice, but I think theyre overpriced, more practical for a business..
I would never buy a combination plasma/tig welder..
leave plasma cutting to the plasma cutters, and welding to the welding machines..