The exhaust on my TBSS is stainless MIG'd together with mild steel wire. Still holding strong after 8 years? Totally fine.
This ^^^^is my point. Once you can figure out the heat range, wire speed, and puddle control, then making very functional welds is not that hard with a little practice. When I bought the 110 mig I pretty much wasted a 5lb roll of wire and figured out what I can and can't do with it. It took about a month, but ....it was fun. I know that I can get 3/16 cold rolled steel welds to be very strong, and at 1/4" it isn't hot enough. Once we started putting a turbo on everything in the driveway, the little, budget mig became invaluable.
I have a friend that does tig work for us that makes it look like it was done with a machine - he's truly unbelievable. He's a master with aluminum and thin, crappy metal. But the tig work isn't needed most of the time. I say this and I'm looking for a tig for my garage presently, but only because I want to learn how to do it and then I can do aluminum exhaust on the cheap.