I have used the one I built about 4 years ago, several times with success. Its limits are ambient temperatures. I can't use it at all up here in the bay area. Its just too cool out. But in Salinas, I did at least 5 different pulled pork cooks, along with a few failed briskets ( my fault) and ribs.
I never had issues with any plastic melting, and I didn't have to make any modifications. It really made cooking pulled pork about as easy as one can imagine. I refilled the pan with wood once, half way thru the cook, and that's it.
All in all, it has it's limitations, but it certainly no gimmick. I did have a bit of a challenge finding a domed lid, as apposed to a flat saucer style lid. That definitely helped. And, the raw materials aren't as cheap as he lets on in his show. If you live in an area with an abundance of terra cotta, then you might find some deals, but I think I ended up shelling out close to $75 for the ceramics alone. But the nice thing is my temps never fluctuated once it got going.