I have the Hot Sock-ish diffuser from Sally's and I love it. I picked my blow dryer based on the fact that it came with its own diffuser so I was really annoyed to find the diffuser constantly falling off. The mitt stays where I put it. I have a standard sized dryer and my daughter has a little travel dryer with the wider opening but I've used the mitt on both with no problems.

Yes, if your hair touches it, it sticks and feels weird...but I try not to let my hair touch it.
3a/b, fine, lots of it