Here is my opinion.
I use to be a certified welder years ago and modern welding techniques have come miles with better methods and welders in general. With shielding gas, it controls the process so complete and almost zero splatter and porosity. Non sheilding mig is alright for heavier metals, but a poor choice for thin sheet metal and especially on restoration work. Butt welds can be difficult with blow through and with better control with gas, just makes it easier.
Here is a link from Kevin at Eastwood, and if you don't want to watch the entire video, go to 6:30 and he covers his opinion with not using flux core on restoration.
https://www.youtube.com/watch?v=BNmAU3xeCHIIt is a good start for a beginner and I would suggest to your buddy to spend some time with some good welding sites and just watch with an open mind. weld.com is one, as this guy has a bunch of good videos, lots of it is tig, mig and testing different welders and giving an opinion.
I first bought a Lincoln 135 SP and it was equipped with gas. I tired the flux core right out of the box and again, it is OK for heavy material, but the shielding gas is so much smoother puddling and little clean up, other than grind it down smooth. Not near of a chance of porosity with gas either. I use a 75/25 mix of argon and c02. Straight c02 is cheaper, but more splatter.
Research is the key. Good luck