It's probably best to do those types of drinks post resistance workout rather than before because the taurine in those formulas with everything else that's in there ( also when you're liklely to do your big carb and max out hypertrophy by carb injectioninto the muscle fibre) is goood recovery fuel and glyco top up.
If it was cardio you were asking about though ..now that would be a different story .
yea caffeine is ergogenic, it stimilates your CNS and will make you more alert aswell as enhance endurance.
Caffeine tabs is way more efficient tho and costs only a fraction of a red bull can.
They are fine as long as you get a lot of water. I also find that energy drinks in general make you really dehydrated. I used to get headaches while working out because I didnt realize that my body needed water after an energy drink.