Yes, I have taken to force-closing the app in that way (along with disconnecting the VPN up in the notification area) when I no longer want it around, but that's not really what users are supposed to be doing on Android.
Rebooting isn't a way to close it. Even if it's not activated, it and the VPN are present in your notification area upon every reboot.
I completely get that most users will want it to start automatically and will want it running all the time, but I wish it also had a mode where it behaved more like a regular app: when you run it, it's in effect (if you have it enabled), and when you exit it via its menu, it's completely closed. It sounds like that's what Sergey might be working on, which is great.