Glocks are good to go in my book. As are hammer fired HKs and Berettas.
The P99 probably is too unless the striker block gets stuck up or something. If the striker block were to stick, it would absolutely fire on decock.
Compared to a Beretta which physically rotates the firing pin out of the way of the hammer and, well there is no comparison. HK and Sig decockers are similarly robust but I can not totally recall their action.
Finally, you can absolutely “decock” a P99 just like a PPQ with a hammer blow to the rear of the slide. This is less of a deal in the P99 since it is simply decocked at this point and can still fire DA.