The quiz at the end of each lesson on the NihongoUp website is so bloomin’ fantastic. It’s really effective. The questions are challenging and diverse enough to really make you think, recall what you have learnt, and apply the knowledge. If you get under a certain amount correct you have to re-take the quiz afterwards, giving you time to go back and check the lesson, read over notes, etc and look at the content and information to make sure you understand, then return to the quiz - ensuring that it remains in your head. It’s actually quite good getting it incorrect a few times as it gives you that golden opportunity to brush up on the learnt material and really solidify it in your brain. It is also very useful seeing all the answers available and recognizing what is actually incorrect or wrong; in turn helping you remember and recognize what is correct in future - the quizzes are very well laid out in that they are randomized each time you take them and they also do not give you the correct answers or wrong answers afterwards, so it ensures that you cannot simply just guess or put less work in. You have to be very confident in your answer and knowledge learnt.
I found by the end of a few of them I had a much better understanding and had actually learnt fully how a certain thing works; a particle for instance, or numbers - and I have since been able to recognize them in other texts, or utilize them. The quizzes themselves hit on only very important and key elements of the lesson, so they are things that you should definitely have learned and therefore need to remember. There’s no unnecessary content. It is very liberating and satisfying to see, learn, remember and then understand and be able to use this knowledge in the real world.