I don't like it on the slide - MUCH easier to manipulate a decocker on the frame...
I don't like decockers on the slide because they dig into your hand when you rack the slide. I also don't like combined decockers and safeties. Don't like having to unactivate the safety after decocking to use the DA mode. Also, wish more decockers were like Sig...gently dropping hammer as opposed to letting it rip full tilt into the firing pin safety.