I've had it a couple of times.
Ironically, my insurance company covers the treatment if done in a hospital, but in hospitals in the Netherlands, they have a policy that everyone gets a certain amount of botox 'on the hospital' but not more than that, and the amount you get is pathetic (like one vial/year). Still they don't give you more, even if you (or your insurance company) are willing to cover the cost (which would still be about half of what you would pay in a decent private clinic). Long live the welfare state! (something to think about for you 'Mericans before public healthcare is launched). It's quite ok, just as long as you only break bones and have heart attacks but don't have anything that's a bit rare. With HH, basically I'm paying for insurance, I pay rediculous taxes that for about 1/3 go to healthcare but if I want to get botox, I still have to pay for it myself...
Anyway-->I've had three treatments in a hospital and one proper one in a private clinic. Palms, which was completely useless (10 injections per palm) and crazy painful (only emla anaesthetic, didn't work). The pain was really bad...it was the first time the docs did the treatment then and they felt really bad continuing with it but hell...after a couple of injections then finish it, please. The sweating in the treated areas definitely improved a lot, but as my fingers weren't treated, the overall effect wasn't great of course. I would say it took about 4 months for the sweating in the treated areas to gradually return again.
Then I've had injections in my arm pits and my feet. Didn't work at all.
Then...I wanted to give it one last chance and paid EUR900.- to get the treatment for my hands with the doc that treated people in one of those hospitals who don't take patients anymore but do give the right treatment with 50+ injections/hand. This guy treated people on the side in his private clinic (ethical?...doubtful), but obviously, my insurance company wouldn't cover that...yes really...anyway, covered it myself and at least the guy was skilled doing the treatment, I expected a world of pain with my previous experience in mind, but with ice cubes it was surprisingly painless, except for some finger tips. The results were ok I guess (don't expect completely normal dry hands, some areas are absolutely dry but some still damp, I would say it works for something like 80% in absolute sense), but all in all, since my HH is pretty generalised it didn't change my life that much to say wow...this is the solution. So, I didn't go back.
Also...they say Botox injections have no systemic side effects, but I'm not completely convinced, nothing serious, just dry mouth and stuff...maybe it depends on how the injections go I don't know. As for cramps or loss of strength in the hands I had none of that, maybe if you use it for years and years, but really two days after the injections you can just use your hands like normal, maybe a small bruise here and there but nothing painful. Interestingly Botox does not only block acetylcholine, but also CGRP, VIP and SP...but that's just a technicality.
I would say it's worth to try it once...see what it does for you, even if you have to pay it for yourself. It's relatively harmless and convenient, apart from the initial minutes of pain and the potential cost. In any case, make sure you get something who knows what he's doing, it can be REALLY painful but that's completely unnecessary.