Pah – I should have known the 820 would be released as soon as I bought something else. I’d concluded there wasn’t going to be anything between the 500 and the 1000
What do you actually want to do with it?
If it’s performance tracking (Heart rate monitor/Power meter) and live segments then the 520 looks good. It will link to your phone for automatic updating of Strava and so on.
If you want to navigate routes you’ve plotted or downloaded you need something with better mapping. The Edge Touring is a bargain if you don’t want heart rate/power (although you can get some with the Touring plus for a little more) and don’t mind using a cable and a computer to upload your rides.
If you want navigation AND live segments you need to look at the 810 or 1000.