Enh. I've always been a bit leery about energy drinks. Most don't do anything for me anyway (though Bawls gave me the shakes), and I try to limit my caffiene intake (well, until I started this new shift, but I'm going to get back into my normal intake next week). I'll sometimes grab a Monster or a bottle of Bawls because I like the taste, but it's rare.
My old coworker used to swear by 5 Hour Energy and Monsters. Towards the end of my position, he'd start the day with a Monster, have one at lunch, and probably pop a 5-hour sometime in the afternoon alongside another Monster. Thankfully he tossed in some water here and there.
Caffiene wise, supposedly a 5-hour only contians the equivalent of one cup of coffee, which is around 100-135ish mg per 7oz serving for drip. A full can of monster is just more than twice that. So, I ballpark it at him intaking the equivalent of a pot of drip coffee in caffiene a day.
The main draw comes from the vitamins and other additives, presumably preventing a crash that comes with something like coffee or excessive carbs/sugar while contributing more alterness than caffiene alone. Though it has a hell of a lot of B-vitamins in it.
Anywho. I can't say I've ever really had the urge to try it. When I drink something it's for the taste, so unless it tastes good, I tend to not drink it.