Two weeks of testing the Demo OpenHAB Server configuration on a Debian powered BeagleBone:
Tons of power-off reboots and all works fine.
Only one time it refused to connect to the outside world.
Stability: 5/5
Security: 5/5
(I finally found the documentation https://github.com/openhab/openhab/wiki/Security + added the Android App + cut the port forwarding)