I bought the gorilla for my brother and the brown werewolf for myself.
Personally, I love them! They come with foam pieces you can use to make the fit snug. You'll want to put some black foam or fabric inside the mouth to give it the best effect.
I've tried mine with Vaseline on the teeth/mouth area for that wet-slobbery look.
Takes a little prep to make sure it fits right, but once it does, it's pretty darn cool!
Here it is in action! http://youtu.be/-zGtx8NwQno
Their YouTube channel has great little how-to videos for making the mask fit and last.
Hope that helps!