I'm 18 years old and I tried Powerfull a few months back. I myself, did not experience much in the way of strength gains either. I was guessing that it was due to my being 18, so the natural testosterone boosting properties didn't make as big a jump in testosterone as it has with other, older users. Cissus, on the other hand, is great and helped get me through and heal very painful forearm splints without even stopping my training.
I'm sure the effects are different with everybody because there have been some great reviews of Powerfull, but I didn't seem to have as profound effects as some others. Age aside, however, I could also just be a non-responder to Powerfull, which every supp has.