Use for mountainbiking?

If you want to record HR, then connect the Fenix as external HR sensor to the edge and at the beginning of each activity (on the Fenix) go to Menu - Sensors - Wrist HR - Broadcast HR. This will broadcast HR to the edge. You should only start the activity on the edge, it'll record GPS, HR, cadence, speed, etc sensors, and at the end it syncs with Garmin Connect and the fenix

Ah I see, so you're planning to use the edge kind of instead of using komoot on a phone. I did not try that (I don't know how it works with the navigation if you don't start the activity) But I can tell you from personal experience that it's useful to be able to see whatever data you have without having to lift your hand from the handlebar and look at your watch. I also don't see any disadvantage of using the edge for both, I think you can even have half screen map and the other half with data (didn't try though) I use it mostly to "document" where I rode and the few times I used it for navigation I had a full screen map and changed between the screens by swiping left/right on the touch screen. I find it very useful. This is my 1st real bike computer (the previous one was 30 years ago and only measured speed and distance)

I dont need much information while cycling. For me it is much more important to see map from the Explorer. Measured information like average speed etc. is something that I review after rides at home. Of course I will record the ride with Explorer but will do that with Fenix also especially if I get more info from it. Do I?

I think that the only info you get from Fenix and not from edge is the HR, which can also be broadcasted. And if you connect the sensors to Fenix then you'll have everything there.

Ok. So Explorer measures after all quite a lot info for my requirements. I think I will be very pleased about the purchase. Thanks for the answers.

I have a similar setup as you (just a forerunner 965 instead of your Fenix watch), and I actually record everything on the watch. All my sensors (external HR monitor, power, speed sensors) are connected to both my watch and the edge devices, so I have all info on both. As you mention, the watch contains more data than the edge (for MTB for example, the MTB metrics are not available on the edge, and won't appear either on the watch after syncing if recorded on the edge), and this applies to other features. So I start the ride on both devices, but at the end of the ride I save the watch one and discard the edge. Hope this helps! :)

Ok, so I'm going to stick to my original plan. Thanks for your answer.

I use fenix plus explore 2 for mtb

The fenix is started at beginning and stopped at the end, during the ride is in my pouch.

The edge is used during the ride because of the larger screen. At the end the edge ride is discarded.  The edge doesn't give anaerobic and Aerobic effect or trainning effect only trainning load. That means that after true up sync the fenix only calculates trainning effect. This fenix calculations is not updated  in connect so the bra is white not orange or green 

Besides edge doesn't have mtb or e-mtb profiles. 

I use OSM maps because I know that my trail edits are there in the next month. 

this makes no sense IMHO, because you won't have the HR recorded and most of the performance stats are based on HR