After a couple years of searching/waiting I have finally found a UPS that works with the IdPi.
PiJuice:
https://uk.pi-supply.com/products/pijuice-standardBasically you just connect it and it works (with basic functionality). I have been using it for a week with no issues.
If you install the PiJuice software it is very configurable including 3 buttons that can be customized to do pretty much anything.
Since users can't add software to the IdPi it would be great if JRiver considered adding native support for it. I suspect there's quite a few users are interested in this. Please consider.
I can add some photos and notes about the few customizations that can be used on the IdPi when time permits.