I've been using that setup for the past 5-6 months and it works very well for me. There is not a ton of room in the "expandable" panniers but I carry my change of clothes on one side and shoes on the other. The main compartment is two sections and I easily carry my lunch, spare tube, multitool, lock, cell phone, and keys with room to spare.
My favorite feature is the sliding system: just pull up and lock the bike, slide the bag off and go. Oh, and that you can easily carry a six-pack on the way home. :thumbsup: It is a very good value IMO.
Hope that helps.
Matt