This may have been mentioned elsewhere and so I apologize if there is a similar thread already existing.
I know this is by no means a small suggestion, but I feel like there are missed opportunities to use kanji from previous levels to learn new kanji. The Radical > Kanji > Vocab system works really well, especially when starting out (I’m only at level 6 at the moment). But I feel like as you build a repertoire of kanji building blocks, you can use those AND radicals as mnemonics for the new kanji.
As an example, we learn 花 (flower) using the radicals for flowers, leader/person, and spoon. Then in level 6 we learn 化 (change) without any callback to 花. I don’t mind that we learn “flower” before “change,” but it’s seems like a missed opportunity not to use our previous knowledge to solidify the new concept (especially since in Japan the idea of transient and ever changing flowers could have been the logic behind the kanji).
The radical system is great for mnemonics and remembering the structure of the new kanji, but isn’t always the best for explaining the meaning of a kanji. Using already learned kanji could help us learn the new kanji and reinforce the old material.
Again, I know this would be a large effort to add to the lessons, but perhaps it’s something to think about in future updates. Keep up the great work!