I tried it, I found everything you said true _at the beginning_ but after a few hours as it wore off I paid the price for the initial boost and the net effect was near zero, or possibly even negative.

I've also been around a ton of people who are taking it constantly and well...they act weird, a bit more frenzied and not necessarily more productive on deep thinking tasks. Not sure if this was the case for me. It's an enjoyable experience, like a recreational drug. I see why people take it, and further I see why people believe it helps them be more productive, but I am highly skeptical of these claimed benefits.