I have one of the ebay "turbine" half-mask models. Only bummer is that I haven't had a chance to try it out because I'm STILL waiting on my electrician to finish hooking up my new booth and AMU. So, I really don't have anything all that usefull to say about that.
Up until now, I used either 3M or Gerson OV-rated cartridge-style disposable respirators. The DO catch iso's, but there's no way of knowing when it's saturated and stops working. So, IMO, ok for once-in-a-while, buy the mask, spray, and chuck it- type situations, at least with 2k products, anyway. I just wouldn't trust them past that. Not when you can end your career by trying to get one more use out of it.
I do still use them when spraying solvent-based paints, airbrushing with solvents, or pinstriping with urethanes. With those, you know it's time for new ones if you can smell the fumes (well, preferably sooner). But, unless you're really careless, they will provide enough protection, and save you from dragging around another hose.