damn vix, you did get a good deal.
my first kit came with the 15% bleach, which was tolerable, although after about a week of wearing them overnight, my mouth was about as raw as the thawed out steak currently in my fridge. it's definitely not a thing your teeth are going to enjoy, but it does work. i got a refresher kit with 20% and that felt like it was going to disintegrate my teef so i had to trade them back in for the 15%. you have to have some seriously insensitive male bastard teeth to handle the 20s.