All pre wrap really is is a cushion for the tape so that it doesn't rip your skin off, and its soft so it cushions whatever you need it for. It's great for rips, ankles, wrists, etc. I use it on my rips all the time, though they have been getting bigger and worse so I stopped. I think it works...
If you don't freak yourself out, you won't fall off. Unless you mess up. In your head, (this is what I do at meets) tell yourself that you won't fall off. It usually works cause if you don't then you'll probably scare yourself and fall off.