I used to use them, but I stopped when I ran out of three packs.
They cost a good bit to be unreusable...
I order mine from DRobbins Wholesale company by the bulk cause it's much cheaper that way.
The routine I used to do is that of Dan Garrets where you tear a napkin and have a kid do exactly as you do. You dance around a little and then shove the napkin in your mouth. The kid does the same.
Then you pull the napkin out and start pulling the mouth coil as well. (The kid tries and has nothing). When you reach the end, you pretend the coil is stuck on something, so you have the kid slap on your back and you pull it out with a large sponge tooth (which was compressed in your hand the whole time.
Make a few corny jokes like:
"I think that was my wisdom tooth because all of the sudden I am feeling a little dumber!"
"The whole tooth and nothing but the tooth!"
"I can't wait to see what the tooth fairy leaves me for this!"
etc. The jokes are too easy to make up.
Yes the jokes suck, but lawsuits suck even more. Here's a tip. Don't let the kid shove the napkin into his mouth. Why? It's not worth it to have him choke. Simply shove the coil in your mouth, retaining the pieces. If he starts to do the same, grab the pieces away from him, adding yours to it, therefore you end clean.