My kid did a few Outschool things several years ago (Minecraft, I think rather than Roblox, and maybe some other coding-type stuff).
They were fine, he enjoyed them. Nothing sketchy and the "instructors" were decent with kids. They were offered at random times, but it seemed to be most fun when he joined on a consistent schedule (say, Wednesdays at 4p) so he'd be playing with the same kids.