Thanks for your answer!
It would be better (in my opinion) to have reviews for each rule of every grammar point. Because right now, if (for example) I have difficulties with the past negative of the polite form of u-verbs, I will fail only on the (let’s say) 5th SRS lvl. Then the next day, I will be asked the specific sentence I failed the day before, so I will easily remember it and then I won’t see this grammar rule for a few weeks, potentially (because the time intervals become bigger).
So for now I added some custom reviews.
Nonetheless, I really like this app. Thanks for your contribution to my learning experience and I will definitely become a paid member in a week when my trial ends!