We really had a lot to complain about Garmin Firmware quality in the last years. But from my experience the latest version 26.18 for the Edge 840 is really very good. Thus I want to give a big shout-out to the Garmin Edge firmware developers and testers!
I have been using 26.18 for ~4w and my experiences are very positive:
* no crashes
* very low battery consumption: only 31% battery consumed on a 155km/9h gravel ride with
- 2y old Edge 840 device which has been used a lot
- routing enabled following a course
- live-tracking enabled
- notifications enabled for smartphone apps (WhatsApp, Signal, Rain Alarm,..)
- RTL 515 Radar Tail Light controlled by the Edge 840 via the Connect IQ app "Smart Bike Lights"
- battery saver mode disabled
- satellite systems: auto select
These are the only minor negatives I experienced:
* the bug with the "switch powermeter prompt endless loop" is easy to work-around by disabling BLE in the PM sensor details (and only use ANT+ for the PM)
* boot-up is a bit slow, takes ~40s from power-on to the main-screen, but this is still acceptable
Before I would accept any future firmware update to my device I will carefully read the changelog of the new fw version and would only consider updating the fw, if any of the fixes or added functionality are really important for me.