We have an RD40F and an FD75. Running them on an S680 and S780. I've had some issues with the FD but they are almost entirely related to the fact that it was damaged and repaired, poorly. The RDF is incredibly complicated compared to the FD. Several gearboxes and drivelines etc. Both have their areas where they do a better job cutting than the other. The FD handles short beans better because of the cutterbar/reel relationship. The increased lift height of the FD is nice for going over mailboxes, gate posts etc. We have a couple fields we have to twist the RDF in and out of. I'd really like to try an FD240 or better yet a plus model.