I can tell my thoughts only, as I don't have my ID anymore, courtesy of some Pinoy somewhere...

Anyway, the padded back..It's a nice feature to have, and it didn't make the bag 'soft' or anything like that. The padding was sewn into the bag, so you don't have a chioce to remove it. The think that I did notice was, because of it's shape with the added stiffness, the ID maintains its shape more, and doesn't conform, or 'drape' into your hip as much. I don't know if this is an issue for you or not, it sort of was for me, because in my situation here, I'm constantly dealing with crowds, and crowded sitations with not much space. I found the ID would 'stick out' a little when wearing it, so I'd have to be careful going through store aisles, othewise I'd maybe end up knocking things off the shelf.
I wore it mainly on the Absolute Strap, I tried the Q-AM, but I was looking for something simple. With the Q-AM Strap I had trouble with the excess straps hanging off. The padded back might take up some room, as far as space goes in the zippered main compartment, but not much. I'd say go for it and get it. It's a great stylish bag, useful with the organization and the pockets, and with the build quality, it seems like it would last forever. I wore mine daily for about 8 months in Hong Kong, and for about a year here in the Philippines, so I feel like I know of what I speak!

Be sure and go after the bag color you really like, you'll have it for a LONG while!
Cheers mate, and good luck,
Dave in the Philippines