I tried it just a few minuets ago and it worked pretty well. I could feel both my hands temporarily transform into hoofs and my legs and feet stayed like a pony's until it told me to woke up. I can still feel the horn though which is pretty cool.
EDIT: Well now I'm starting to get small headaches, I'm sure it's nothing since I frequently get headaches, but I don't think it would be wise to try this again. It was an interesting experience, nonetheless.