I lucked into a Hobart AirForce 250 at a pawn shop for $175 and snapped it up.
It has done everything I've asked it to do.
If only doing sheet metal and occasional 1/4 inch, it's a great "name brand" entry level unit, even at $500 retail.
A while ago I had a used Pak 50 which quit on me the second time I used it.
I didn't care for the way it was put together as you really couldn't "open the hood" to troubleshoot.
...and even though the company answered all of my correspondence, they never really gave me any useful advice on testing things that were inside.