Many of the pre-workout NO2 supps have a ton of caffeine in them, as well as a bunch of other shit that may or may not do anything.
NO-Xplode makes me blow mud-I'm done with all of those drinks. Amplify is on the way, and looking fwd to trying it out - I hear good things about it.
BTW - The main active ingredient in most of the pre-wo drinks that increases your NO2 is the conditionally essential amino acid Arginine. It's cheap too. You could just take 3000mg of that and some caffeine - that's what I did for a while.