My SW/LFS has one of these that's a 4'x4' and IMHO, I didn't like it. The view is really distorted. These tanks have to be PERFECTLY level too or they end up with dry patches on the sides.
My lfs has one of these. I think the dimensions are like 18"x18"x12" or something close to that. It's a reef setup with shrimp, cardinal fish, small horseshoe crabs, etc. It looks really nice.
My lfs just sold one he had for display for $400, i came soooo close to buying it, the only problem with these tanks, and why sold it, is keeping it clean, algea grows inside and out, especially on a reef set-up like ha had. Beautiful tanks though.