Roughly, the ideal state is from Theta to Delta- I don't know if a metronome will really synchronize your brainwaves (binaural beats do, however) but what I would tell you is this: If you are going to attempt AP using a metronome, incorporate some sort of ritual like Robert Monroe used to do, and then, when you've conditioned yourself to associate the ritual to achieve the state, try to use your ritual by itself to achieve the state without using anything else.
Whether it works or not, becoming dependent on external cues is not so good. I have a BWGen and Hemi-Synch, and I use them occassionally if I'm having a dry spell or if I just want to meditate and don't want to be bothered by background noise- and I usually project not when I'm listening to them but later on or the next day.
So, there's nothing wrong with trying it, just don't let it become a crutch.

ps. I deleted the other duplicate posts.