Because of the clips, the tool pouch can be moved from bike to bike. My blinky light fits on a strap on the pouch so the light moves with the pouch, saving on the number of lights as well. Extra clips are sold separately but are relatively cheap.
The pocket on the flap can be used for your keys. In addition to a mountain bike tube and tools, I can fit my wallet in the medium size in a pinch. There is an expansion zipper that adds about an inch in length. I have one pouch for my road bikes and one for my mountain bikes.
The clips do not fit all bikes. It does not fit thudbuster shock seat posts. There also needs to be 6" of clearance above the rack or tire so may not fit if the seat is low or there is a rack.