I've been using an S800 (the predecessor of the the 810) for a couple years now.
I like it well enough that i don't see any reason to change.
Battery life is good, the 810 is even better.
It readily pairs with everything i've ever paired it to. 3 different hrm's, 2 cadence sensors, 2 speed sensors, a power meter, a smart trainer, and a watch.
The routing is pretty straight forward, and it synced with RideWithGPS and Strava with zero fuss. make routes, boom they are there in the app. finish a ride, boom its on strava. The Bryton route builder is fine too but not as easy to use as the free RWGPS.
I recently traveled from the US to Germany for a week of work and took a bike with me, I downloaded the German gps file from the Bryton website into the computer and the routing/navigation worked as flawlessly as it does in my hometown. It even understood a couple of horribly pronounced shops and cafes in the voice nav.
I like the group ride feature, although I only have 1 friend who has a Bryton computer that it works with and I hardly ever ride with him so I haven't gotten to use the feature much, it was neat to know he was coming along on the route without stopping to call or look at my phone for his location.
The only mild complaint / learning curve I have had with it was being patient and understanding that I had to turn on the computer, let it boot up, THEN turn on my phone app and let it fully boot and connect before selecting a route and riding off or i'd be grumpily fiddling with it on the move. I don't know if the S810 uses your phone as its major source of data like the 800, but it can be slow/laggy to give you reroutes at times.
I do kind of wish the S800 had strava live segments on it, but not enough to go out and buy another computer.