ive got yellow HF one, for couple of years, so far so good, only sliding hammer is POS and failed right away, got another us made sliding hammer, i use HF studs as well.
I bought the yellow HF unit for a $100 two months ago--it works just fine.. Just take care of it and keep things clean--and it'll do ya just fine..
I read in some other places that it's great for "hobby" use--but if you pull lotsa dents--you should put some of that dent-pulling money into a nice quality stud welder..