Might I recommend MaruMori instead? It was created by people that did WK, and thought they could improve on a few things. People that are active on this community, MaruMori has a thread here (MaruMori.io & Kitsun.io - [UPDATE: Mobile Apps Beta!] - Grammar SRS, Grammar Lessons, Reading Exercises, Vocabulary, Kanji and more!). There are a variety of opinions on which one is better, but I did the MaruMori trial and liked it, I’ll buy lifetime at their next sale probably. The link is marumori.io
Best of luck with your studies!