Regularly get nuisance calls. A couple a day average ? And yes I am registered with the preferential telephone service. I'd ignore unknown and withheld callers normally, but it's difficult if you are expecting calls from folk you won't know.
I was planning to get a CPR call blocker to go with my existing phones (because obviously I don't want to replace them). But I read somewhere that they don't work with multiple extensions and folk need to replace with a wireless system ! I felt that this couldn't possibly be so, it being such an obviously deficiency, so I asked the question on their website asking if their product had this issue. I'm still awaiting a reply weeks later.
I guess CPR's answer must be, "Yes, our product isn't well designed and is of limited use, but we don't like to admit it; and we don't care about developing a reputation for ignoring customers."