My boys are 9 kg in weight and are 10.5 inches in height, so we bought two of the large ones so that they can move around if need be. They only ever sleep in the crates, and on their insistence they both sleep together in one. The other one we keep in my husbands 4x4 for when we go visiting overnight or longer. See photo below
I would not be without the crates, and to be truthful they'd not cope without them either, they feel safe and comfortable in them. No matter where we go, the crate goes with us. I have the crate in one of our lounges, the big one that we use more than our second lounge,