I had a P-Rails on the neck of one guitar, though it was only set up for two sounds, not three, and I was never quite sure what those sounds were because I didn't wire it. Probably humbucker and P-90. But it sounded great and they are very good pickups.

To me they just look a bit awkward on a guitar, both in black and in cream. It's probably possible to fit a nickel cover on them. A solid cover and drill the holes for the P-90 screws yourself, as they won't be in the same place as on a standard humbucker, they'll be more central. But that's just me.