I have two of the 25 gallon ones and I just upgraded to 40 and 45 gallons. I had the 25s welded by a guy I found on the local classifieds. He warped the hell out of them and didn't do a very good job but even after the crappy welding they didn't rust once I repassivated them. The metal is thin, 1mm is about 18 - 19 gauge, but I am all electric so it doesn't really matter. I'm not sure how much different gas is as I haven't brewed with gas since I was doing stovetop.
For the price they can't be beat, I got a 40 gallon and a 45 gallon plus all the fittings I needed and welding for the price you would pay for one Blichmann 55 gallon kettle, and Blichmanns don't even come with a wort-in port. I mean really? They say "redesigned from the ground up" but you still have to punch a hole to attach a sparge arm, and drape a hose over the side of the boil kettle to sparge? Weak.
Sorry for the rant. In summary the stainless if fine, its made in China but so is just about all the other stainless you buy in the states.