Why isn't there a 33% option for your test? What if I'm pretty certain that 1 of the answers is wrong, but have no clue which of the others is most likely to be right? Then my confidence is exactly 33%, and I have to either overestimate or underestimate it. The 50% and 25% options seem to cover the other two versions of this scenario (I can eliminate either 2 or 0 of the options almost certainly) but this appears to be a gap.

(incidentally, this only occurred to me because it happened to be the case for the first question on the first of your quizzes...)