The thing about a lot of branded pre-workout supplements is that they have "proprietary blends" and don't release the actual sizes of their ingredients on the labels. True, people pretty much settle on amounts and post this online, but the products are always being redeveloped and it's just a hassle to keep up with it. What I'm hinting at is that if you do use pure DMAA, start low and work your way up just to be safe.
Pure DMAA will feel like a pretty good stimulant the first few times you take it. I think it feels "smoother" than any of the branded pre-workouts, including jack3d. You'll have energy and focus and all that other stuff that's written on the advertisements. The problem, though, is that tolerance grows and you need to keep taking more and more of the supplement to get the desired effect. Not only can this become cost-prohibitive, it can also unleash some of the negative side-effects of DMAA - some bodybuilding-specific, and some stimulant-specific (such as not being able to sleep, annoying comedowns, etc). It is also psychologically addictive, and some people who take it for a string of workouts feel like their first workouts without the stimulants are sub-par. Price will be cheaper buying it wholesale, and you don't have to also dose the exorbitant amount of caffeine that's typically always paired with DMAA in the store brands.
As always, just keep it around as another tool in your arsenal of plateau-breakers. I have it in there alongside headphones blasting thrash metal, a spotter who knows my lifts well and I trust to let me safely push my limits, some strength-training workouts designed to push through a plateau, and so on. Things just will start getting kinda weird if you use DMAA too often.