I have the Garmin Dezl and there are things I like about it and things that I do not. They all have their pluses and minuses and personal preference would certainly come into play when choosing Garmin or RM. I'm sure both units are capiable.
One of the reasons I went with Garmin was the ease of map updates which are good for the life of the unit and the extensive POI files that exist. (Point Of Interest) There are literally thousands of possibilities of files built by users on the web. You download the POI files on your computer and transfer them to the Garmin via internal memory or a memory card plug in. As you travel you select the POI catagory like campgrounds, breweries, ships, wineries, diners drive in and dives, state fairs, Wal-Marts, museums, literally most anything of interest is out there in a file. You select a catagory and it tells you within a radius what is within range. You just select one item and it gives you a route from your current location. I do not know if the RM unit has this feature but there are many discoveries on the road that we would have cruised by had we not had access to the POI files.
Later Ed