Tried to get both orange and redder forest mangosteens from two different sellers this year, but finally got only the more orange type. Fruit from one seller were smaller and had almost no flesh at all, so I'm commenting only the bigger ones from another seller. She collected them from the forest somewhere in North-eastern Thailand.
The good:
Taste was pretty good, similar to purple mangosteen with maybe a little bit of banana mixed in. Some fruits were just sweet, some more sour in a nice way - sweet tampoi kind of sourness. Size was good, medium mangosteen size with thinner peel.
The bad/weird:
The flesh sticks to the big seeds, and where flesh ends and seed area starts was somewhat fuzzy. There was some latex (at least near the seeds) which sticks to the teeth and seems to change taste sensations somewhat, eg. noodles eaten after the mangosteens tasted weirdly bitter.