I use magnesium oxide as a laminitis supplement, its on their website and seems to have done wonders for my girl.
Regards the calmer bit, I have no experience of this, my girl is naturally chilled most of the time, and she has not become more horizontal, thus I do not think its affected her temperament in that sense to any degree.
i bought some to help chill my 2 year old as naughty wen plaiting.i used it for 10days it did make a differance.i was told spillers cool mix had good trace of magnesium in .
Not used that one but have used Nupafeed on our restless, out-of-work-since-March Irish TB and it has worked where everything else failed. It's also Mag based.