Application firewall vs mandatory access control(apparmor)

Hello. I am trying to isolate ksp game from connecting to the internet, because I do not trust new eula and redshell -privacy. I could find only one app firewall: Douane, but I do not trust it, because it is new and does not come from official repos. Group with firewall dropping every packet worked, but I do not like it. Apparmor looks like the best option.

1)Does apparmor slowdown my game? 2)Main question: Which is better? P.S. You can see that my english is not the best -short answer would be appreciated.