Hello Georgs,
I've got that system. That is, the GPSMAP 840xs and GMR 18HD radar. Mostly happy with it. I'm sure it's a learning curve, but I almost prefer my old RayMarine B&W Pathfinder radar back. The GPSMAP840 is definitely an improvement over my GPSMAP541s. But I'm still trying to learn the best way to tweak the radar. As I said, I'm sure it's just a learning curve for me. I will also say, Garmin, Like Chevy or Ford, seems to only want to use their products. Ie, I already owned a lot of Garmin Chips and software, so it was pretty easy to just continue on with the newer, bigger and better versions. But if you don't already own the software and various chips for more in depth plotting, be prepared for some sticker shock. That being said, what comes on the unit does a good job. Colby