If you mean the aerodynamic seat bag, it's *huge*. My wife has one and it's got enough room for a full bladder, rainsuit, extra pair of sandals, all the repair accessories, food out the wazoo, and a bunch more. Plus the two straps convert it into a sort of backpack off the bike.
Or if we're on our way to a local tour, it'll hold her helmet and shoes, food and water bottle and sandals. Only downsde is that it has no organizational pockets.
Can't help on the panniers, but I bet they are nie as well.