Typical in IXP but not as well documented as iBGP route reflectors.

If I get it right, ideally, they reflect the eBGP routes but not adding their own ASN (transparently); they calculate the best route on behalf of the participants (“Maintain a separated Routing Information Base (Loc-RIB) for each peer configured as RS-client”) and they can also filter bgp routes in/out but like they were the participants.