Overall doing my reviews in HH is quite smooth, but one remaining point of friction is how often I provide an answer that’s correct, but not among the alternate answers or synonyms included in the item. Recently I was trying out Maru Mori for Japanese study, and that site has a feature in its reviews that I think would be great in HH: when you’re marked “wrong” in a response, but your answer is actually a correct synonym, there’s an option to “mark correct and add to answers / add to synonyms,” so in a single action it adds your response to the acceptable response list AND marks the answer as actually correct. Very handy!