Those are two different use cases for me. A radar detector is much more specific. Waze replaces the usefulness of other drivers flashing their lights at me.

Anecdotally, people rarely seem to do that today for whatever reason. I expect at this point people think I'm either trying to cuss them out or complain about how bright their headlights are today, but if you see me flashing my lights there is a cop ahead looking for tickets.