Obviously I haven't the faintest clue........ not being in a city and not being UK ........
Clay soil drains poorly. It'd stick around for a time. But be degrading all the while.
Poo is poo. If it works for dogs, it'd work for cat. Yes, yes, yes I know - they are different, as are their diets. But, were I you, I'd try it.
Keep in mind, we are all obsessing about cat poo when we flush billions of tons of our own down........
Still, every little bit counts. I won't compost my own, but neither will I fuss excessively about theirs. The cat feces will degrade easily. Along with the dog and the horse and the cow and the goat and the fox and the birds and the moose and the bear and the everything else's poo........
I worry more about the litter. So much volume. It also degrades, if handled correctly (i.e. not put into plastic and sent off to the dump).
I know they say not to put animal waste into compost heaps. And I know I am lucky in living where I do (places to put such not being a problem). But, yes, go with the doggie poo composter. Try it anyway.