Whether or not you should get it depends on cost. That's funny that peyote is the only legal one there, it kinda sucks though since the other fellas grow 5-10 times faster and are impossible to kill (I've cut them down until the only plant matter left was about 1 cm below the soil and it lived and in fact 5 of them sprouted out of the stump).
If you're not too experienced with psychedelics I'd eat 6 buttons my first time (assuming this is your first time with mescaline) to test the waters. It's a low dose in all likelyness (not neccesarily though, it depends on the strength of the cacti) but it's the only way you'll be able to test it out. Afterwards I'd probably raise the dose up to 8 and then later up to 10 or 12 if I felt that 6 was not enough. I've heard of people getting good trips off of 6 buttons and I've also heard of people getting great trips off of 12, so it's really hard to tell you how many to take. Also I don't know how large these large buttons are in comparison to the stuff I've read about.
Mescaline is great man, it's got the best open eye visuals of any psychedelic I've done except for DMT. I've always found the trip to be wonderfully gentle and mind opening, it's a psychedelic in the true sense of the word, it can show you everything you need to see.
Also, don't be scared off by vomiting or anything, but do have a place where you can throw up and not have to do a bunch of cleaning later. I've thrown up tons of times on mescaline, and it's never bothered me. It's made my trip better a few times, like when my vomit appeared to be rainbow colored sounds and other undescribable stuff.
One other thing I'd like to recomend- smoking DMT while peaking on a heavy mescaline trip is one of the best combos I've done. Seriously, it's super cool. Just a suggestion. Mescaline is a very welcoming drug with a lot of wonderful properties (in my experience of course), but you might as well start low to keep everything exactly how you want it.
