Charging for a service is fine, but I agree that it is legitimately insulting to charge for use of a consumer-owned device.
That said, what wattvision lists in its FAQ is extremely fair. Using data from the last three months is free, so if you want to do your own processing you can easily download from there even if the device is difficult to directly access.
That said, what wattvision lists in its FAQ is extremely fair. Using data from the last three months is free, so if you want to do your own processing you can easily download from there even if the device is difficult to directly access.