The best feature is the battery save

There are other bugs with the 820 series as well, including but limited to - bluetooth issues with Iphone connectivity to garmin connect app, text messages not consistently appearing on the screen, device crashing mid ride after 100 miles (data lost), device locking if you try use zoom function on map screen, unreliable "IQ" feature

Overall, I count this as a very good upgrade, although some features could be a lot easier to work with.

The 820 has some nice features that I would miss:1

It has great features, but it is so buggy and underpowered in so many respects that it's constantly frustrating to use it

Automatic features sometimes work and sometimes don't.

It's nice that there is an accident alert feature as well.

I love the size and the robust features on this model

The 820 sounded very promising and has some great features, however the execution falls far short.

The 820 is a nice unit and a nice package with some great features, but it is not stable

Let me tell you that this is not an easy feature to set up

and I love the battery saver feature that 520 does not have.

As it is, it seems more like the feature was developed for a impressive demo and then forgotten

Then, it started to recalculate the route even though I had that feature disabled.

I have really loved the extra features on this computer plus the small size

Great features and works as expected.

But the features I do use are AWESOME and keep my rides interesting.

it might be a great feature for the trainer, but not out on the road.

... Ties in easily to speed/cadence & heart rate monitors, Bluetooths easily to my S7Edge, automatically uploads, great stats for analysis, very good notification features...

So I loved it during those few months where it worked as it should most of the time.