Controversial opinion: I'm so glad I did WaniKani
Various threads supporting or disparaging WK seem to come up every now and then but now that I'm several months past my WK journey*(see footnote) I just briefly wanted to share my thoughts. Oerall I feel like I'm extremely grateful to my past self for powering through (most of) WaniKani and also grateful for the team that put it together. But it's not perfect.
WaniKani pitfalls:
1) Nonstandard radical names. "Wolverine," "Poop" etc are kind of silly and don't really fit with RTK schema.
2) Example sentences are generally terrible, and don't have audio or furigana. Most example sentences are like insider jokes and I didn't find them helpful. In fact I ignored them, but at least they didn't slow me down.
3) The mnemonics to remember complex Kanji don't build on other Kanji that are already taught. For instance, 慨 (sigh, lament) is taught as being comprised of as soul忄, root 艮, and fang 牙, rather than more simply as soul忄and already/long ago 既. I can learn "the soul of long ago" as "lament" very easily but soul-root-fang doesn't make any sense without coming up with a contorted and overly complicated mnemonic. That is just one example but there are several like it.
4) Additionally, I find the web-based interface and needing to type the answers very cumbersome. There are various methods to bypass this thankfully.
5) Not a con per-se, but: It's important to note that WaniKani does NOT teach you how to read Japanese. That takes hundreds of hours of practice after finishing (or while doing) WK. It also doesn't help at all with talking.
6) Monthly fee. Many people feel learning materials should be free but the monthly fee is quite reasonable in my opinion. I have no problem buying books/audiobooks/etc and WK is no different. Fortunately I have a career and am older than most people here I bet so the nominal fee is not an issue thankfully.
OK, now on to the pros:
1) It is a standard system where if you power through and do your daily dose month after month after month you will learn most jouyou Kanji.
2) The vocabulary might seem esoteric sometimes but overall I think the words are carefully chosen to emphasize both Kun and On readings, as well as irregular readings that are in common use.
3) You end up with several thousand useful vocabulary words and have the ability to read new words without much difficulty. For instance, the word 死体安置所 is not in WaniKani as far as I know, but the individual Kanji's are all pretty basic and I was able to read it and deduce its meaning in the context of a book without losing a beat. Death-body-peace-put-place - in other words, a morgue. All with standard On readings.
4) Some of the mnemonics are pretty good. I might have laughed out loud a few times.
Recently I've seen a few posts saying either asking "do I need to learn Kanji" or "Kanji is slowing me down" or "I can't remember Kanji." My answer is that Kanji is absolutely essential and once you know common Kanji learning new vocabulary is orders of magnitude easier. So if you are having trouble with learning Kanji, then WK is my first recommendation.
And finally, I'm sure WK is NOT the most efficient way. Cramming RTK and reading a ton is probably more efficient, and if I had to do it over that might be the optimal way to do it.
It took me about 14 months to do WK (see below). I have been learning Japanese for a little less than 2 years (about 19 months) and I can now read most books with the help of Yomichan. Read about 12 books so far in 2022, currently reading a long mystery. I'm a slow reader, read about 6,000 cpm when going smoothly but aim for 100% comprehension. Mined about 10,000 cards and have >2200 unique Kanji in my mined deck for whatever that's worth. I feel that I owe my solid base of Kanji to WK - thank you!
*Footnote: I completed about 50/60 lessons in WK. At that point I found that it was no longer worth it time-wise as I would rather spend the time reading in Japanese and most of the "new" Kanji I had already come across reading. Good luck!