I looked for details and found no mention of bandwidth metering. However with all those Windows Updates that can hit GBs a week across a few machines I have little doubt it is very easy to hit 50GB a month today. Yes, you claim you have no Windows Updates but with all the malware out there and the recent Conduit outbreaks plus I can't be sure of your WiFi security it looks like the answer for now is no. There is no way to check this given the Bandluxe device.

Normally I would suggest using our own router with that router having a bandwidth meter and daily limit controls in the router but the Bandluxe information was so sparse I can't offer that.

I think, in this case you want to disable the WiFi and get wired to only the select few devices you can control.
Bob