With RealJam, you're basically paying to get the scenes new on release, as the aggregator sites get everything on a delay of at least a month. They also do bonus BTS videos. It's worth it for me, but that's because I think they're in the running for best studio out there and I like to support good work directly. If you don't care about the delay, you're not really missing much.
Badoink/VRCosplayX/18VR is only worth it when they do their big holiday BOGO sales once or twice a year.
