I'm going to have a problem if it bases my riding on the last 5 miles of my ride. Why wouldn't they evaluate the entire ride?
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Using short term average consumption to estimate range is pretty much what can be done unless your route/ weather conditions are known. Although I agree with the rest of your concerns this one is unjustified.
Don't worry about or trust the estimate too much. Instead of range a much better signal is your consumption in WH per mile . Nyon shows this , I don't know if Cobi does it.
Also range is greatly affected by how you ride, the riding position, wind etc. Someone mentioned Domane+ range, unfortunately that will not be indicative of your range if you are riding fast. There is a very significant consumption difference between the upright riding position and 2.4" tires of allant and a road bicycle like Domane+. I rode with several very fit road bikers several times 30+miles, I was able to pass them at their peak but when we compared my rider input to their watt meter readings it turned out that at speeds 24+mph we were both pushing equally hard and we were in that region for most of the ride(granted I was also carrying lots of stuff, even a full sized bike pump while they were all in lycra with very light full carbon bikes). So at higher speeds most of my support was wasted in inefficiencies due to riding position and weight.
And that 85-90mile range is hard to believe, it translates into less than 7wh/mile. If you are going very slow and/or turning off the assist frequently maybe, but then what is the point of an ebike.