I really like the Jalup app! I have completed the Beginner deck and almost completed the Intermediate deck.
If you’re using WaniKani then you don’t need the Kanji deck from Jalup. Just ignore it. I have tried it a few times and I really like the WaniKani way of teaching Kanji more.
The Beginner deck starts from 0 and builds your Japanese up 1 word or concept at the time. Along the way, you learn grammar and vocab. I think you can start it at any time. There is some duplication of content, but that’s just because you learn some frequent and useful words. The 100 first cards (100 out of 1000) of the Beginner deck are free. My advice to you would be to try the first 100 cards and see if you like it. If you like it, you can buy the remaining 900 cards. If you don’t, then at least you have learned 100 words from it 