The new Legacy PM only needs power from a transformer, and is connected directly to the track. I power my Legacy PM with a 180 brick.
The Legacy PM, the way it is designed, can be controlled by a Cab1, Cab1L, or Cab2.
You lose the ZW's handles with the PM, making is a bit harder to run conventional (my thoughts). If you need all 4 channels (tracks) to run trains the ZW will be cheaper, otherwise the PM/brick combination is cheaper. You will need one PM/brick per track.
The ZW has volt and amp meters.