How does this hassle users more than regular captchas? The only additional effort it adds is a bit of thinking (too much to ask these days?). You don't have to type anything and it replaces the "Submit" button so not even any extra clicks.
> how many permutations of different questions are there?
Infinite! Just this of the possibilities with that kind of system. You could keep adding different questions (just minor variations) and it won't be difficult to keep ahead of spammers. Plus there is always a trade off between security and ease of use. I think the ease of use with clickcha is well worth the slight loss of security.
I am the developer of clickcha. Appreciate the input, but you seem to be forgetting that bruteforcing can be avoided by temporarily banning the IP for some time after certain number of incorrect attempts.
Of course, there would be alternatives for people with disabilities.