DMAA is chemically almost identical to speed. It will rev you up for your workout, no question, only to have you crash hard afterwards. It will sky rocket cortisol levels and lead to adrenal fatigue. In the long run, you will be worse off supplementing with it.
If you are looking for a boost before training, drink a small cup of black coffee. If you need anything more then that to train, you need to re-evaluate your training and nutrition big time.