Do not dryfire a rimfire pistol. Damage to chamber and firing pin will result.
I've always heard dryfiring a gun is bad for it, especially on a hammer-and-pin operated action. To my knowledge dry firing the striker operated P99s won't harm them, but I still don't do it, both for functional reasons and safety reasons.
But today I decided to install my +3 followers in the P22 mags, and they don't utilize the follower buttons that are required to trip the slide catch once the mag is empty. So, after the last round is fired, the gun would cycle, leaving the chamber empty and hammer cocked, which would lead to a dryfire unless I was conciously counting as I shot. I'm thinking they may not be the best thing to have if they're gonna cause dryfires.
Guess I'm sending the +3 followers back, or selling them on ebay.