I had mine done about 8 years ago and it honestly didnt hurt much at all, just a small nip, like if you give blood...

It can wear the enamel off your teeth but that more comes down to placemnt of the piercing, if its far enough back in the tongue its not so much a problem. Can wear the bottom inside gum where the bottom ball rests though, although my dentist says mine is OK. I have chipped a couple of teeth by biting it not long after I had it done but thankfully not done much damage.

I love mine and would be gutted if i ever had to lose it for whatever reason.