For my 1st session (2 weeks and 2 days ago), the pain was a bit worse than tattooing. I can't relate it to some dude going in with a jackhammer 6 hours into it, tho.
From what I've learned so far, the different frequencies are for different colors, and the 1st session is the most brutal. I can let you know if the 2nd session is any better at the end of Jan. My motivation to get something fabulous to cover the old tattoo easily gets me through the pain.
12 treatments??!! Are you looking for blank skin or just to lighten and open up the cover possibilities?