So it seems the take-home message is that you can use the app without issue to change settings, but dont try a firmware update (?)I bricked my bike trying to do a firmware update so agree that the experience with the eTube app for that purpose may not be ideal! The problem is that the app corrupts the original firmware in trying to write the new version, so if the update fails you can't access the bike wirelessly. I had to visit a Shimano service centre to get the bike un-bricked and the firmware updated. I certainly wouldn't trust the app for firmware updates in the future. Unfortunately the alternative requires buying a 'black box' from Shimano (and an adaptor to allow the provided cable to attach to the display if you have a bike with an EP8 motor) at a total cost of nearly £200.
Using the app to change settings on the bike has not caused any problems for me so far so I'm happy to continue to use it for this.
HTH
Cheers
Iain