I have been using the Optipower Ultraguard all this season and it have been prefect. I am running a Power box digiswitch with a 850mah 2s as the main supply. I have the Ultraguard setup with the Fasstest telemetry through the Futaba 14sg. I have set a warning for low voltage on the rx. The digiswitch runs at 5.9volts. Anything lower the 5.7 will activate the alarm. See video.

https://www.youtube.com/watch?v=75Hoih2X72g