Jack3d is a great product if you don't care about health. If you do try and find something without the 1,3 Dimethyl and more B-Vitamins rather than massive amounts of caffeine. I take Vasocor by Katalyst and its amazing! Massive pumps, amazing focus and no jitters! and Its Kre-Alkalyn instead of monohydrate for staying away from the bloats.
I agree jack3d is good. Just watch how much you take.I started running out of energy and getting real sloppy on my last sets. Then I started taking this stuff and was charged up and noticed I was stronger the whole workout. Only take 3 times in a week and you should be safe.
I think the general opinion (if you haven't made up you mind yet - its been almost a year!) Is that Jack3d is good, BUT its all down to the individual. I have done 1 tub in 7 months. I only use it if the thought of not going to the gym on a gym day creeps into my mind, not because of the ingrediants that help (or not) you gain muscle. Going to the gym and eating properly will do that anyway - to a certain degree.
For me, Jack3d worked initially but I quickly developed a tolerance for even the maximum dose. The pumps were none too significant and after trying it 4 different times during the past 2 years, I have gone back to my tried and true favorite pre-workout, Superpump Max. Jack3d did give me the energy to get through the workout but I feel like I've done better with a strong pot of black coffee.
Like the other posters say, it really is an individual thing. Some people swear by Jack3d and some swear at it.