A couple years ago I was asked to interview via CoderPad and while I appreciate their attempt at having emacs and vim bindings, the fact that they're not actually accurate was worse than using Google Docs.
That is, it's actively worse to be almost your editor of choice than I think it would be to obviously be a "clumsy editor". In the former case, the interviewer perceives you as poor at writing code when you're fighting with a slightly drunk editor, while in the latter (like at a whiteboard) the interviewer adjusts for the environment.
Edit: the interviewers let me retry via projecting my screen while using emacs locally in a terminal. I hope CoderPad has improved it's key bindings since then, but I hope interviewers test out these editing environments before assuming people would be 100% proficient.