I'm not sure I'm very comfortable with people using C2 as a "test" - I think you'll just select for people who can quickly figure out how to use an app they haven't seen before. That kind of person will appear to do better than someone who is slow at learning to use new software, even if they are overall better at whatever qualities you're really after. People familiar with other OSs like Mac and Linux may also be unfairly disadvantaged. And of course if someone has used C2 before and keeps quiet about it, they could seem amazing!
Imagine a complete genius at game design who conveys everything by sketching pencil on paper, but who's useless at using C2. Surely you'd still want to accept them.