The Lezyne S-Caddy has a host of compartments to house your spares and keep everything organised. We managed to fit an inner tube, tyre lever and CO2 cartridge with head into the main compartment with relative ease, with a multi-tool stuffed in for good measure. There is a small Velcro compartment underneath the bag for a multitool but it’s only sealed with Velcro, leaving it fairly open to the elements.
Fitment is simple with two Velcro straps looping around the saddle rails and a third securing the bag around the seatpost. The only complaint is that when the bag is stuffed and a little weighty, the Velcro did let go a couple of times around the rails especially after about six months’ use and being swapped between bikes.
Well designed and easy to use, but Velcro isn't perhaps the best choice for straps when the bag is full and the weather is bad.