The "pocket" has probably been reviewed before, but what the hey...
It's black textured leather, nice and supple, quality stuff. Lined with smooth cottony-like material. What does not show well in the pix is the 3rd piece that runs down the front. It's 1 1/2 inches wide and covers a separation in the front half so that the trackball never gets touched at all. Which is nice but it increases the thickness by 50% (3 pieces instead of 2).
Fit is excellent, once you fiddle around with it and loosen it up. It goes in and out nicely (I don't have BSE on it but that should be no problem).
Magnet feature is nice of course. It has Blackberry embossed on one side and the logo on the other, looks classy. And when you put the Pearl in you can see Blackberry on the top of the unit in the thumb cutouts on both sides.

I've used the Seidio rubberized for 2 plus months now, keeping it in my hip pocket or on a cupholder cradle in my car. Here's the difference for me:
The pocket is noticeably bulkier and a little heavier. I noticed it right away. It adds 1/2 to the width (the sewed seams of the halves) and probably 1/4 inch to thinkness. So if you're a "pocket guy" like me you may want to leave the leather pocket alone. Of course you have to grab it and pull it out every time it rings, but you knew that. I think it would be ideal for putting in a purse or bag.
My take is if you value minimal thickness/bulk go with Seidio. Also if you don't want to mess with taking it out of something to use it. The Seidio is pretty plain looking.
If you value a classy looking leather cover that shows off the logos and like to whip it out and don't mind a little extra bulk go with the Pocket.
EDIT: Now that I've used the pocket for a month I like it more, because it covers the entire front. The case doesn't cover the keys/pearl at all. I got used to the slightly bigger size. And now I'll be able to use the new Seidio battery without getting a new case. It's a good issue, and cheaper than the Seidio by over half.