Can't tell you for sure if it's sharp or not. I got some advice to not use it because it MAY be sharp for corys, but the deciding factor for me was that eco complete has no nutrients of its own out of the bag, but just helps absorb and release them with time.
About capping though, I also got advice that capping eco complete with something like sand is pretty useless as the eco-complete pieces will begin to come to the surface. Especially with corys digging. But since several people above haven't had problems with it hurting corys. I think you should just decide from an aesthetic point of view. Also, my understanding is that eco complete pieces are pretty varied in their sizes, and won't provide a very uniform surface. However, again it's up to you whether you want that look.
Seemed kind of a waste of money to me since I was planning on capping with sand anyways and didn't want the eco showing.
Good luck though
Last edited by behemoth; 10-11-2015 at 02:59 AM.