Hi,
I bought Edge 840 recently and I am discovering differences between FR265 and Edge 840 when I do indoor cycling with Smart Trainer and what's really disturbing - FR265 shows more and better data than Edge 840.
Activity: Indoor cycling
Training: My own training created in Garmin Connect
Smart Trainer: Technogym Ride with power meter (ANT connected)
Activity made on Forerunner 265 has visible "Target power" graph included in Power graph and also specific "Intervals" where I can see all the "Rest", "Ride", "Cool down" phases of intervals.
Activity made on Edge 840 has just normal Power graph and I can see only "Laps" which are not distinguished to each other, instead of "Intervals".
The only thing Edge 840 has and FR265 has not is "Stamina" feature. Otherwise FR265 generates better output in saved activity.
Just for explanation, the first pic is FR265, the second one is Edge 840, two different trainings, but both of them made the same way. And also, there are some drops in connection to power meter, I am aware about it.