I have downloaded GlassWire onto my two PCs, and three Android mobiles. My experience is mostly positive but one of the mobiles is a fairly old Motorola Moto G which has Android 5 installed. GlassWire works well except for the fact that it constantly uses between 40% and 50% of my CPU.
I have tried clearing the cache and deleting the data but the only thing that stops it is to do a forced stop but the problem is back again within a few minutes. I have also tried uninstalling and reinstalling but still have the same high CPU usage. I do not have this problem with the Motorola G4 nor the Wileyfox Swift 2 Plus both of which have Android 6.01.
I have had to uninstall it from the MotoG because the high CPU usage made it virtually unusable.