The app has already had an update although it seemed to work pretty well beforehand.
I'm not too sure that regular changes of the power settings are needed though. Thats what the gears are for.
I live in very hilly South Devon (Torquay) and I find that level assist 2 gets me up all of the hills I encounter whilst providing a good range. I think that the torque sensor helps; acting to feed more power in when the going gets tough. Obviously, 3 is faster up hill but it uses up the battery more. I have experimented with level 1 but I found it to be less fun so I haven't used it much other than to go easy on shared use paths. It would be of use to conserve battery, though, if I was going further afield.
On the flat, I'm able to exceed the 15.5 assist cut off which makes the assist level irrelevant. On slight downhills I can exceed 20 mph - the standard higher gearing of my six speed helps. In fact I made a point of checking the units on my app speedometer as I thought that it may have changed to kilometres. It hadn't. By the way I am 69 years old and only moderately fit these days.
I find middle gear on the hub gear to be very useful on slight inclines. I can trim it using the derailleur, and an increase in effort is rewarded by a surge from the electric motor. Again, I guess that the torque sensor is doing what a torque sensor does.
Also, the bike freewheels surprisingly well. Locally there is a lane with a long stretch of slight downhill that leads into a slight uphill before another downhill. Over the years, and on many different bikes, I have tried, but never succeeded, to get enough momentum without any pedalling to get past the slight uphill bit and onto the next downhill. I actually managed it the other day on my Brompton Electric. I don't think that weight is too much of a factor as my hybrid Dawes Mojave was a bit of a lump itself.
It's not all been plain sailing. I have had a replacement motor. Both my nearest dealer - The Bike Shed Exeter - and Brompton were excellent though.
So, Ex Brompton Man, I recommend going for the third time lucky. The only downside is the cost now compared to what you probably paid for yours.