It can be a problem especially on a USP where the slide serrations are relatively shallow. I wouldn't know about the P7. Kraigster, you've not had this problem with your Glock before the serrations are significantly deeper. If you want NP3 on a USP you might consider having Robar mill the serrations a little deeper.
Its up to you if you want the internals done. They won't do springs and will plug the barrel to protect the bore.what don't they NP3 when you send them your pistol???