I prefer the design of the PS1 and it has so many compartments to keep me organized. I can keep my wallet in the front compartment, checkbook in the zipper pocket behind the wallet and the rest of my stuff in the main compartment. I just think overall it is a much cooler, chicer look. Oh, and the leather is gorgeous and soft and slouchy. I have no regrets with spending big money on my PS1. And the PS1 can also be worn cross-body if you want to...
As for price, the medium PS1 is $1,595 and I can't imagine the Mulberry being too much less than that. The Bayswater is $1,000 and this looks bigger, so the difference would maybe be a couple of hundred dollars.