Also, note that the succubus using its kiss on PCs is likely to be the exception, not the rule. The most likely result is that the _NPC_ whom the succubus seduced beforehand, the old-fashioned way, jumps to its defense and uses the shield-other ability to protect it. That's how a succubus would generally be encountered: as an already-present actor in a scenario, who has worked its magic on an unsuspecting victim as part of the adventure background. The PCs are there to find and expose it, while being hindered by NPCs who would normally be on their side.
People seem to be assuming that the succubus will use the kiss on a PC, without any prior interaction, as a way of defending itself. I'd say that the succubus will rely on its pre-existing target for that, while using its other powers -- flight, change shape, dominate, etc -- to fight the PCs. Note also that the charming kiss can only be used on one person at a time, so that's another reason why it wouldn't kiss anyone willy-nilly.