The Atlas, so far as I can tell, differs from the PSI Polaris only in the very top of the pen-- the knurling is different (the polaris looks a bit more elegant and has two small bands instead of one big one).
That, and the Polaris is available in black titanium, whereas WC only sells black epoxy, 24K and Rhodium. I have a black epoxy Atlas with a dark green flecked celluloid blank that looks great and I use it in one of my seminary classes for taking LOTS of notes (with a Parker Gel refill). Great pen.