It's all pretty much individual taste
Sounds like the P4 is a great unit and hardware extension of Reason! External USB plug included.
Since the OP stated "Please consider Reason is not my only DAW", it's worth adding some of those additional items.
Given the choice of touch sensitivity, and speed dial, I'd buy the SL MKII again right now. I also use the controller along with another DAW, so that's why it's worthy to bring some of those features to the table.
Some may feel the Novation Automap is a pain to have to hit a button to bring up on screen (though it can be resized and stay on the screen if desired). Others may feel that seeing mapping on a computer screen is a hell of a lot better than the small (but still clear) screen on the P4. To me the screen on the P4 looks "toyish". Still, it's all about personal taste. I'm almost in favor of the toyish P4 screen, but I can't say for sure. You get the point though.
Maybe Props will one up everybody and come up with their own hardware controller, but nobody including Borderline should wait if there's no announcement.
I don't think anyone can go wrong with either of these two controllers. They both perform as advertized.