On my engineer I made an "Ultrasafe" Gnomish Transporter. It was great because I could instantly teleport to Gadgetzan from anywhere in the world. It had a few little glitches, though. Sometimes I would transport to the right location...but about 500 feet in the air. This ended in a very long fall and quick death. I have also gone into dimensional flux, turning randomly into a gnoll, kobold, or murloc.
I have also gotten a debuff saying I was replaced by my evil twin. As far as I can tell this does absolutely nothing. It is extremely rare to have any of these problems and I still loved my transporter. It just makes life a little more interesting.