I have a decently sprightly, fairly new desktop setup with a Skylake cpu at 3.3 GHz and enough fast DDR4 memory running under W7-64.
GWCtlSrv.exe and GWIdlMon.exe together use 2.5%-4% of the cpu, and GlassWire.exe uses another 0.75% (when minimized) to 10% (when running the graph).
This is a lot of cpu to have running in the background all the time, even when minimized. It will feel like you are computing with the hand brake on all the time. For example, it uses more cpu than my browser with 20 tabs open, autoupdating some active content.
With a little tablet cpu, I can imagine that it is unbearable and I would close it soon.