I had a Champion GI for a while and put approximately 800 rounds through it before I sold it. Great gun, it fed everything I put in it, and the factory mags, McCormick Shooting Stars, and Colt GI surplus mags all worked fine. Zero issues or malfunctions in the time I had it. Surprisingly the action was verrry smooth, especially after about 250rds or so. I sold it to help fund a CCO, but I wish I still had it. I never modified it other than putting a set of thin Alumagrips on it.
The only annoying thing about it was every 6th rd or so it would bounce the empty brass off the top of my head or forehead. Extractor probably needed some sort of tuning but I didn't want to mess with it as reliable as it was and just left it alone.
Based on my experience, my brother-in law bought a Stainless GI, and had all kinds of problems with it. It would hardly ever go through one mag without a malfunction of some sort. Even with my mags that worked in my GI. He sent i back to Springfield, and it worked great when he got it back, but he was upset about it and sold it. I should have bought it but I don't like stainless on a GI, just sort of wrong IMHO.