I always wanted to try those but I've also always been a bit scared.
In Thailand itinerant pickers will sell them at the roadsides, the problem is that the arils(?) sit in buckets of water that isn't bottled water.
I want to try them but I don't want hepatitis... so I always skip. You can buy them canned but I imagine fresh is a lot better.
I was told the people in Thailand who have them growing on their land seldom deal with the palms, instead they wait for these itinerant pickers to show up. The pickers pay the landowner some cash, and then climb the trees, pick all the nuts and sell them on the road typically within site of the tree they picked them from.
A beautiful relative of the coconut, of course, the one that really interests me in that group is the "double coconut". Also supposedly a very slow and tedious grower. Sadly the Garfield Park Conservatory in Chicago lost theirs (which they claimed was the largest one of its kind under glass) after their greenhouse was trashed in a freak summer hailstorm.