I have owned 3 810s in short succession. The first would not pair with the heart sensor. The second would lock up and lose data on rides over about 8 hours (drove me nuts losing all of the data I just spent 8 hours generating. Finally the third unit seems to be working as expected. Thanks to REI for taking the first two back so graciously.
I find the interface to be usable but not as easy to use as my car GPS.