The 406 Crystalyte is a direct drive motor. Fairly heavey it puts out a claimed 350w not 500w, the 500w is based on on consumption .ie. current imput,
ebike.ca give details and some nice power charts.
The Crystalyte motors are agricultural in build, but last well.
The 406 gives a top speed approaching 28mph at 36V in a 20" wheel, they also out perform most advertised, ( I'm thinking of E-bay here ), 1000w motors for all round ability. Unless your going to fit them in a streamined velomobile there is little point going above 36V you get little extra for increasing the voltage.
In short a good but perhaps a little old fashioned choice.
The Suzhou Bafang bpm motors are available from several suppliers on E-bay and make a good alternative to the BMC motors.
Team Hybrid were offering some high powered motors which should also do.