This stuff is annoying, I find it good for things like coming up with loads of ideas, because it's like new trains of thought leading to other trains of thought changing every 10 mins.
But as soon I sit down to actually do something like coding, I find myself completely involved in it, my attention is focused, but I just keep adding new things or rewriting bits intensely and what should have been something simple and straightforward has suddenly turned into a much larger and complicated project.
I find this constantly going off on tangents happens when I'm reading science journals too, which on the one hand helps me read a load of stuff, but also can feel like after a few hours I'm wondering what the fuck my intent was when I started.
It also gives me this shitty sense of urgency that I have loads to do and can't waste time and I end up getting sort of paralyzed by constantly hopping from one thing to the next as being the one I should start doing, or I'll get 5 minutes into something then do something else, or get distracted, and at the end of the day I get fuck all done if I'm in that state.
Really doesn't suit me for productivity, except extremely small single doses which are subtle enough to be an improvement on caffeine but not enough to cause shit like the above ^ or make me so anxious I need a benzo.
I don't think this class of stimulants is ever going to produce a perfect functional productivity drug, free from shitty side effects.