So I started doing kanji when my Japanese level was much, much lower than what it is today, after 14 years of study and over 10 years in Japan, where my work environment is in Japanese. My wife is monolingual Japanese, too. Naturally, I got better.
I’m not writing this to show off or in an attempt to pose as a “pro” (whatever that even means for language learning). I’m just giving you an overview of my development over the years, and what I believe that means for what I’m going to say.
When I was at a crude, intermediate level, able to converse in daily life, but still always at a loss for words, I was at my height of studying kanji. You can see, my WK account goes way back. At the time, WK seemed to be the thing to do. Learning new vocab while memorising the kanji seemed like a complementary activity worth pursuing. And I believe it was. There are of course drawbacks like vocab that’s obscure or weird, or words nobody writes in kanji, but overall, it was helpful.
I took a break. Forgot some kanji, somehow picked up a few by immersion, and when I tried WK again, none of the vocab items were of use anymore. My Japanese was already at a point where I could tell when something was shoehorned in, and the glacial pace meant I’d have to spend months repeating stuff I already knew, because I had forgotten the odd kanji I’d already burnt. Needless to say, I stopped after a few months, again.
Years after that, I returned with the conviction to do it all, anyway. By then, I had already reached fluency with the rare blackout when a word wouldn’t come to mind, at about the rate it happens in my mother tongue. Now things felt even worse, because I had picked up a LOT of kanji otherwise, and I evaluated WK’s worth for someone who could already get through daily life with almost no problem (there was always the odd kanji I couldn’t read, and it drove me crazy).
Some more years have passed, and what I believe I can now say with some confidence is, the better your Japanese, the better you’re off with RTK. You won’t see anything new, anyway, just stick a character on to existing knowledge.
If you’re really new, study the language itself while doing kanji here. But when it stops working, which will happen at some point, don’t sweat it. Do something else instead, pick up some characters through reading, and if you’re at a level where your main concern is that you mix up kanji in isolation, while being able to read them fine in text – just rush through RTK in a week or two and be done with it. Review from time to time, but don’t bother with SRS. Seeing a freshly learned kanji in a book helps much better with recall.
In hindsight, what WK never got quite right was lookalikes. Not even with plugins. Since RTK makes you write, this will never be a problem.