The D ring allows more pages to fit than than the round ring. I fit a whole Chemistry loose-leaf textbook inside it and could still add more pages if necessary. It lays flat unlike the round ringed binders as well and seems to be pretty durable. I would definitely purchase this product again.
The binder itself is fine however out of three that we purchased in store the label on the spine only peeled off cleanly on one of them. For the other two the labels would only come off piecemeal and they left a residue. We used Goo Gone to get it off but there's still a whitish residue on the black binders that won't come off. Doesn't look very good on a black binder. If you buy this binder in the store make sure the spine label comes off cleanly before you purchase it.