I got given some Universal Nutrition Shock Therapy, used it two or three times, definitely hypes you up, but I am not a fan of the feeling, and my workouts don't last long enough and I feel jittery after my workout so now it just sits in my cupboard.
I should probably do a weekly marathon workout and use it up once a week.
Unfortunately it's personal preference and they affect different people differently, I remember having a pre-workout sample handed out as a body building show (can't remember the brand) I went to and it made me feel sick, as in ready to throw up and completely fucked my workout.
May be see if you can score some samples and try them out before you commit the best part of $100.
Personally I would not bother with them, may be have a strong coffee or a can of red bull before training of you are feeling flat.