Yeah, here’s this too: Wanikani isn't slow
Also, yeah, maybe it’s not the best way to spend your time if you’re already N3 and looking to review specific kanji. That said, there are other tools for that.
I would say that if you start now and reach level 27 before you to go to Japan, you’ll probably be studying more relevant/new material exactly when you’re going to need it (namely, when you start actually encountering those kanji all around you). It wouldn’t be a bad future investment.