I bought a Clarke 151en about 6 months ago which does gasless and gas. I'd only played around with stick welding before when I was a kid so it was my first time mig welding. It came set up for gasless with flux core wire and I used that for a bit but ended up splashing out and getting a regulator and using hobby weld 5 and it totally transformed my welding. If you're a good welder then you can probably get good results with gasless, certainly good enough for chasis welding but if you're not very good (like me) and you want to improve then I think gas is the way to go. There's an article on migwelding where he plays around with gasless which is worth a read. The biggest difference for me is you can see what you're doing a lot better with gas as there's no smoke and splatter to obscure your vision which makes it a lot easier to see where you're going wrong. Having a torch attached to the welder is a great idea, I'll definitely be trying that!
I doubt there's much difference between the cheaper hobby welders, the clarke I have does 30-150amps and having both 0.6 and 0.8 wire I can get decent beads on 1mm - 3mm no problem, it'll do thicker than that as well if you need.