The 810 has the ability to use map.img files to display a topographical map on screen. Also, with the correct file format can display cue sheet information and directions. It has a "get you back to start" capability as well as other useful tricks, including communicating with your favorite social media and bike-mapping and performance websites.
But if you don't want that stuff, buy the 510 if you still want ANT+, or the 200 if you just want on the ride data and post-ride mapping.