I just assumed I would get one when I first bought my MBP. Just made sense, keep it all nice and protected. At least I thought. I was bummed that the new cases were not out, now I think it was a blessing, as I would have gotten one.
But after some time reading etc.. I decided that it just not worth it. My main reason is cooling, and that aluminum likes being open and exposed.
Not to mention I run windows to game, and this is the most critical time it may heat. So I bought myself a really nice stand (Luxa 2) and a fan and let it chill as much as possible. Covering the bottom is just not optimum for it in respect to cooling... Especially if you run it hard and try to use some type of cooling system. That aluminum should be bare and at least raised a bit to open space underneath. Lots of products for that, even with fans.
In respect to protecting it, I am just careful, or use a neoprene sleeve for transport. I think it would be hard to scratch it... Pretty tough case and Im not going to play soccer with it.
IMO it looks and feels so much nicer naked 😀