I used a bottle of it one year over the course of the season. The liner did not have a lot of creosote in it the next spring, but then again it never really does. I can't say with any conviction that it actually did anything to help but for the $5 - $10 it didn't hurt.
I buy the white powder form. I just throw a tablespoon or so onto a HOT fire and that is it. It WILL clean off your pipes so any 90 degree bends you have will fill up with the soot that falls down. That's why i said to make sure you clean out the junk afterward.