Really depends how much is “a fair bit”. I knew about 300 kanjis when starting WK, so the first month or so was only review, then I started seeing new kanji more and more, and around 2 months in everything was new. Overall just a blip in the radar compared to how long it takes to learn Japanese.
But on the other hand, here is a review of someone who did WK after passing the N1. Of course, they had to wait much more to find kanji or vocab they didn’t know
In any case I would wait to finish the 3 first free levels before making any kind of decision. For some people WK clicks well and for some it doesn’t.