I had an 800 and now have an 810. No major differences (except the bluetooth hookup as hippy mentioned and a slightly different interface). This logs your rides via your phone automatically to Garmin Connect but seems to reduce battery life a bit as expected. Also comes with a different mounting that sits in front of the bar. Get the 800 if you want to save some dollar as they're going cheap these days. Wouldn't say that it's worth the extra you pay for the 810.
I had an 800 and now have an 810. No major differences (except the bluetooth hookup as hippy mentioned and a slightly different interface). This logs your rides via your phone automatically to Garmin Connect but seems to reduce battery life a bit as expected. Also comes with a different mounting that sits in front of the bar. Get the 800 if you want to save some dollar as they're going cheap these days. Wouldn't say that it's worth the extra you pay for the 810.