My gf got me one of those, it's heavy as hell because there are so many damn compartments in it. Then again, I only use it on the days I take the subway to work and put my documents and lunch and **** in it. Used to ride with a chrome bag but now I have a vented backpack.

The leather, I suspect will soak up sweat and salt like there's no tomorrow. It's not the same closed stiff leather that is in a brooks saddle like the OP is thinking of.