Rislone products get respect from some people here. The typical response is going to be, what problem are you trying to resolve? How many miles are on the vehicle, the OCI, is there sludge/varnish that needs to be cleaned, are lifters making noise, oil consumption issues, etc? If you are unsure of any of the answers, or you aren't the original owner of the vehicle, and have 50K or more miles I see no harm in doing a little "possible" cleaning as PM. OTOH, knowing the history of the vehicle [well maintained], I see no need unless there's a problem. Opinions will vary.