The freeze is easy to explain by the laws of physics.

When pressure goes down, so does temperature. (The inverse is also true.)

So as the 16 oz of CO2 that are compressed in the tiny cart get to expand, the pressure in the cart goes down pretty fast. Hence the cold. When I use the carts, I never touch them with my fingers, I think it's cold enough that you could loose some skin there. (If you live in the North you know what I mean!!)

I haven't used them so often, but I never had a perfect fit on the valve, still inflated the tire all right. I'd recommend to everyone to have a pump though, because when your CO2 doesn't work for some reason, well... you're stuck.