I just bought one of these. Seems like a solid product so far. It fits my 2014 rMBP 13 like a glove. The materials are like you'd expect, neoprene with some hard rubbery stuff around the edges. There's a touch of excess length inside, but only a very minor amount. There's no excess room as far as height or width.
It opens up on the side, and the rMBP is easy enough to slide in. The magnetic latch stays in place, enough so that you can have the magnetic side facing the ground & the laptop won't fall out.
I think the only drawbacks are a) you have to take the MBP completely out the case to use it (unlike some other case designs) b) because of the magnetic latch, it's longer across than a form-fitting zipper sleeve would be.
Based on my limited experience with it so far, I'd recommend this product. Seems reasonably well made and it certainly fits a lot better than all those sleeves for the Air that are also sold for the rMBP 13.