Peel off the rind. Cut the fruit away from the pit -- it's not a freestone fruit, alas. The flesh is white, juicy, and tender with a distinctly chewy quality. The flavor is light and tropical, kind of like pear or honeydew melon with a faint coconut note, if you're not familiar with lychee fruit. But it's so similar to lychees that I'm not sure I could tell them apart. Very tasty!
Due to the amount of bother in peeling the fruit and removing the flesh from the pit, compared to the small amount of flesh thus obtained, I probably won't buy them again fresh. But I would happily eat rambutan-flavored things, or get them packaged, or devour them from a fruit plate if someone else had done the work of shucking them. If you are a sensory seeker and/or like having things to do with your hands, fruit that requires work to get into is a socially acceptable form of stimming.