They aren't as large as my old bags, but my old bags were junk and fell apart. The material on these feels like it will last a long time. I like that it has 2 inner pockets to keep smaller things organized. The included shoulder straps could be used to strap larger objects down to the top of your rack.
The lower clip to hold the pannier against your rack doesn't seem to be very well designed. I haven't tweaked it much, but I don't think it will do a good job of holding the bag steady. It might not be that big an issue because I don't do any offroad cycling with these.