The RMR and the RMS are both excellent optics. I have had the RMR for almost a year and it has operated without fail. The RMS is lower profile with a crystal clear picture window. The major differences I see between the two are: RMR is adjustable and can be turned off to reserve battery. RMS is always on but the battery tray is accessible from the side. I also like that the RMS sits low enough to co-witness with stock height sights. Both are great options.