The PDW is a sidearm that isn't very powerful, but has a high rate of fire and is quiet for zombies. Additionally, it can use 5 different types of magazines, making it easier to find ammo for it.
Because of it's rapid rate of fire, it is one of the best sidearms to use when fighting survivors. Using MP5SD Mag. and M9SD Mag. makes the gun audible only to players, allowing you to shoot survivors without worry of zombie interference. Even without subsonic rounds, the PDW is still quieter than some sidearms. The only downside is that it takes 4 shots to kill a zombie without a headshot and that it would take a full M9SD Mag. or M9 Mag. to kill a player even if every bullet hit.