Mine switches on DeadSpace2 sometimes, it's nearly impossible to get in a lobby. But when it's normal i get lobbies right a way.I don't wanna screw with mine because i'm not absolutely sure what it'll do. Many gamers say switch to open, blah blah open blah blah open, but what else does having it open effect.Having it open makes joining lobbies easier but what else does it makes it easier for ? Viruses, hacks, crashes.......what? That's why i'm not taking a wrench to anything at the moment.Don't understand it, don't screw with it lol.
It basically restricts who can connect to you and your party etc, Strict NAT will only connect to members with Open NAT I believe and wont allow anyone with Moderate or Strict to connect to you. It will often kick you from games if anyone else with Moderate or Strict NAT joins which makes it a nightmare to play in parties when other peoples changes too. My cousin and I spent 3 hours trying to get 1 game on Battlefield before because of this. Soon as we both switched to open I never had another connection issue. The good massively over compensates for any minor security changes that come from open NAT. Ive used Open NAT for many many years with no issues at all.
You have Firewall and likely a security key on your router to protect from hacks and unauthorised access so open NAT wont affect the security in that regard. I know Open sounds bad as if you are opening a security hole for hackers and viruses but thats not how it works. Its merely a control on who you can connect to and what other NAT types you can enter lobbies with.