I also have the 253 bag with the divider. I can't really figure out what its purpose is supposed to be. It's very close to the bag of the bag, so you can't fit anything big behind it (which might be helpful for organizing things in the bag). And it's kind of floppy, so if you tuck papers or other flat things behind it, it won't really hold them in place. Also, it does tend to hang down a bit, so sometimes when I'm putting something really large in the bag, the divider will get squished down under it, which is a pain.

I guess it might hold a little padding, but due to the floppiness it probably wouldn't hold it very well.

I don't know if it's sewn through the lining -- I've actually hardly worn the bag in the rain, since we've had a very dry spring and summer.

Of course the SuperPro divider might be different that the one that comes with the 253.