I've always heard that caffine/stims and NO supps cancel each other out so to speak. NO being vasodialatory, and stims being vasoconstrictive.

I see lots of supps now that seem to combine these types of things in pre-work out formulas. RPM with caffine and theobromine combined with icariin. NO Explode also comes to mind. I see RPM works, and lots of people seemed to like NO Explode.

How does this work? Any informed opinions or observations?