We went for it to save time.... When our bird was in the avionics shop (took 2 months) we chartered a jet, and with the jet we never got to fly the long STAR that we always got with the PA46. I asked about the reason and the answer was that if you had PRNAV the controller was able to give you a different route, so we looked into the possibillity to get the approval and since it wasnt any big things we needed to do we went for it...We have been saving roughly 20 min flying time every week since then...Huge cost saving for us
The rollsteering is needed if you want to be able to fly on AP, we didnt know at the time that you are allowed to fly PRNAV manually. In the jet we always flew on AP so we never questioned it...However another PA46 in Sweden got the approval with the restriction to fly manual, CAA had something against his S-TEC AP, we have King.