I own a Handler 125 with MIG. Absolutely love it. I've done by and far mostly steel (car repair, exhaust and body work) with it. But, I've done some stainless as well. It does it okay, but I'm not used to welding SS either, so I'm not sure it was the machine.
For aluminum I know its out of the question. I recently found out about aluminum brazing rod though and it worked really nice for this aluminum oil pan repair that I did. I even shot a video to show how my first go around with it went. Just thought I'd mention it as an alternative as most know welding aluminum is 'hard' and pricey.