After reading all the crap about it on this forum, I ordered Jack3d and 1,3 dimethylamylamine from Bodybuilding.com about a week and a half ago to compare.
FWIW - I am 28, female, 128 lbs and drink coffee or espresso (black, straight) regularly.
Jack3d:
Definitely gives you a strong 'tingling' sensation. I experienced this with previous rounds of SuperPump (I go to the gym. A lot.) but unlike SuperPump, didn't feel a bad 'withdrawal' or experience any heart palpitations. Bonus. I didn't drink coffee the first day I took it, I took one scoop (since I weigh less than the average male) and experienced increased productivity and energy days 1-2. By day 3, 1 scoop was not doing much for me beside the tingling sensation and after about 3-4 hours of the last dose I felt like I was crashing hard. Sleepy at 4 p.m. hard. This is unusual.
Took the weekend off- no supplements.
1,3 dimethylamylamine (Body Conditioning Solutions):
Started this on Monday w/ 25 mg. Again, no additional stimulants in the form of coffee or caffeine.
Noticed immediately that, unlike my normal ADD flipping back and forth between multiple screens / conversations/ twitter... I was completely monofocused on one thing and one thing only for about four hours. This was a total perk. No tingling sensation, no weird heart palpitations. I definitely experienced an increase in metabolism, which I wasn't expecting- felt hot in long sleeves and was unusually hungry by lunch. Tuesday same effect. Wed (yesterday), I took 25mg @ 9 and another 25mg around 1 p.m. This was a bit better for sustained concentration but the second round was markedly shorter than the first. This morning I took 50mg @ 9 and, as of this writing (12:30) I feel no effects whatsoever. Just warm/ high metabolism for about an hour and a half and I probably would have gotten a lot more coding done if my power hadn't gone out this morning.
In sum:
Jack3d may be more beneficial if used on an empty stomach. That definitely enhanced sensation. It may also be better if you are not used to a regular dose of stimulants in the form of caffeine or other. For me, the effect was minimal and the tingliness was distracting. The effects were also mitigated after 3 days of sustained use with an increasingly bad 'crash' of wanting to sleep and being utterly unmotivated about 4-6 hours after dosage.
1,3 dimethylamylamine, for actual concentration and focus (for those of us who aren't on adderall) was much better for me. In the future I may continue to use this product but will do so with a combination of regular caffeine intake and will probably reserve it (and, hopefully, its potent effect) for need-to-get-this-done now projects or end-of-the-month campaign work.
YMMV, of course, but this was my experience as someone who comes from a normal coffee-in-the-morning routine.