This tool above I use it quite often, usually 1-3 times per quiz (day), for instance the last time I used it today was when I was quizzed about "busy, hectic" and I recalled "ひそがしい" (wrong kana), I managed to pick the correct multiple choice since was shown as kanji as "忙しい" but then I've realized I had recalled the wrong pronunciation, so I had to go and manually lower this.
This is unavoidable because it is too easy to work around a multiple choice even by accident (like described above), and every time is a lot of clicks to get to correct it, so would be very convenient if the manual control of mastery levels could be brought (trough a button or something) on the page right after you give the answer. If not the control itself, at least a "button link" that sends you to the tool in the image above