Yeah I’ve been taking it for quite a few years. Its VERY well researched and quite alot of benefits.
The migraines may well be from not drinking enough water as has already been said you do need to up your intake.
Generally water weight increase can be about 0.5 - 1kg I’d say!
I have also had issues with an upset stomach/toilet issues from it before but I’ve found its only usually if my GI system is under stress from other things. When this happened I stopped for a couple of months and have been fine since
It wasn’t obvious but I’ve had migraines for a long time and when not taking it but strange that they often returned when I was using it. As you say it’s probably unrelated, so generally drink a lot of fluids but the migraines are probably linked to being run down and when I don’t eat well!
I took it years ago when lifting a lot. Gained a couple kg from it but could do a few reps more or heavier weight than before. I wasn’t aware of cognitive benefits so haven’t bothered since those days.