I read a statement from Masterbuilt stating that thin plates used to keep the replaceable firebrick in place during shipping. The plates will burn thru. I don't know where the "insulation" thing is coming from. Contact MB yourself if you are concerned and get it from the horse's mouth.
The sheet metal used on for the 560 is not the thickest I've seen, however it's not the thinest either. It is double walled, so that's good. Will it be a generational hand-me-down? Likely not, but for $500, it's a great way for someone to get into a great performing gravity fed. Frankly, I'm shocked at how versatile it is and how well it performs and I'm a picky guy. It almost feels like I'm cheating when I use it. Like they say, don't knock it till you've tried it...or at least know someone who has.