Currently only one filter can be used at a time for showing words using a certain kanji, which is all that's really needed in the dictionary when looking at specific terms, but the user setting to apply it site-wide can be too restrictive and it makes learning new kanji more difficult. It's a really useful feature to have for the kanji the filters apply to, but unfortunately I had to turn it off altogether because I kept running into kanji with 0 related vocab to help reinforce readings & meanings in quizzes.
It would be nice to be able to set up secondary filters to guarantee that the terms list is always populated with something. For example, if my setting to filter for "Most common words" returns no results for a given kanji, filter for my known words, and if that returns no results filter for JLPT words, etc. until it can produce some vocabulary.