I think I have used it if it is the product I am thinking about. In fact at the time, people were mixing it with liquid Clen and then applying it.
I noticed that upper abs and the muscles around the ribs (serratus?) became more defined...kind of like when you are holding water and then drop it.
However, my lower abs and lower back are my problem areas, and I didn't stick with it long enough to really gauge how it worked there...or I just wasn't lean enough in those areas to be honest.
One thing was that it burnt like hell. I think I had one of the versions that also had capsaicin in it. My wife accidently got some on her hands one time pulling one of my workout shirts out of the laundry, and it really burnt and irritated her hands.
I stopped using it shortly after.