I use the Micro Cache only for the road, and the Regular Cache for gravel. The Micro Cache just barely fit two CO2 cartridges, inflator head, single tire lever, road tube and a minimalist tool. No room for keys, wallet, or phone. Given the size of phones and key fobs it is not reasonable to expect a small bag to hold them - size up as needed. Good build with quality velcro and zipper. The angle of the straps hold the bag snug under the saddle. The zipper is a bit hard to slide but contributes a lot to keeping water out. Also has a good reflective strap for holding a tail light.
I use the medium lizard skin bag. It is well made and fits my needs perfectly. It all depends on how much you want to carry. Well made bag that stays out of the way well. Just buy the right size for you.....
The description says, in part, ...Micro Cache is the perfect size to carry a spare tube, tools, snacks AND my emphasis added other riding essentials you'd prefer not to carry in your jersey pocket.
That's not remotely accurate. It's eitheror, not AND. I can get a 25mm road tube in it, and 1 or 2 tire levers. That's about it. Or, as I currently do, I keep 3 CO2 canisters (crappy roads & thorns where I ride), the small Portland Works Shiny Object CO2 inflator, a patch kit, and, 1 tire lever in the bag. 50 ci (cubic inches) sounds like a lot. It's not.
Other bits of the description call out the YKK Zipper and water-resistant fabric. It does resists water. As for the zipper, good luck getting the bag open without taking it off of your saddle. The zipper is crap. A tiny bit of road grime or water and it's almost impossible to open andor close without taking it off of your saddle. One has to hold one side of the bag with one hand, and the zipper with the other. Good luck doing that when your fingers are cold or wet.