My guess: I trust the Edge 810 rather because it has more space for electronics and is newer. I need a calibrated GPS system to confirm that.
Otherwise, the FR620 is good to use, updates to install is easy and synchronization works well, except wireless. For some reason, the FR620 was initially connect with our Wi-Fi and synchronize with Garmin Connect, but suddenly no longer. We have checked the settings, the WLAN reapproved for Garmin (just go through the software), but since then the synchronization is possible only via USB.
Unfortunately, we have to send the FR620 now that he ever partially fails. Ie it measures partially still (RF, GPS, Trittfreq), but he does not show anything. Or, alternatively, he indicates, but measures a nonsense (eg, we drive a track that we know well and the FR620 measures lt. GPS only half the distance).
Conclusion: Who is not interfering with the small 5% Deviation generally well served by the device. It does what it should and can be operated well. We would buy in spite of the mistakes the FR620 again because you can not always take a bike computer (Edge810). Maybe the WiFi problem is also solved by repairing. I will report. (29.Okt.2014)