Since you already have the caffeine pills, it probably wouldn't do you any harm to try them. Some people, due to the amount of caffeine in them tend to get jittery, so I'd watch for that. Caffeine, in any form, also raises the heart rate (tachycardia ??), so you may feel your heart beating a little faster, depending on how they affect you etc. I believe, caffeine can also dehydrate, (but don't quote me
), take a look on the internet for caffeine side effects, and if it does state dehydration just drink a bit more fluid.
They may work for you, but if they do, afterwards you could always consider a cup of coffee or some other caffeinated drink just before workouts. I do know that it does help to keep a person more alert which is probably how it helps during exercise, you just get that extra boost which means you workout slightly harder without necessarily noticing it.