I love running a pistol as a primary outdoors (such as getting a gun hit, or having my MP5 goes down mechanically). When I run my sniper rifle and leave my MP5 at base, my pistol is my primary.
Use heavy BBs and learn to shoot well (like out to 100ft and farther), then when guys hear you using a GBB they will likely assume you are an easy target and get careless. You can also shoot a pistol from cover much easier than with an AEG, largely because you don't have to expose as much of your body to get rounds off (only need your hand and one eye exposed as a minimum, with an AEG you expose your arm and more of your head). GBBs also have the benefit of instantly firing the shot after trigger pull, where an AEG tends to wind up before that first round leaves the barrel.