Some of WK’s mnemonics are great. Others, not so much. I think there are two main problems - mnemonics that don’t cover the entire sound and mnemonics where the same mnemonic is used for multiple different sounds.
The first problem is mnemonics that don’t cover the entire sound. English tends to not emphasize unstressed vowels, making them hard to remember, and it really doesn’t help when WK’s mnemonics don’t cover them.
For example, I’ve been plagued by 認める for many months. The WK mnemonic, “meat” is rather unhelpful - is that supposed to be mito or mita? Who knows? I remembered that the “meat” in 認める went one way and the “mead” in 乱れる went the other, but I could never remember which was which, no matter how hard I tried. I only recently managed to start getting it right after coming up with my own mnemonic (you can recognize me by “me toe”).
To compound this problem, WK sometimes uses the same mnemonic for multiple different sounds. To be honest, I have no idea how they could even do this. It’s such a basic and obvious thing to get wrong.
Luckily, WK’s mnemonics for onyomi kanji readings are pretty consistent - “road” is always ro, “roe” is always rou, “rowboat” is always ryou, “robe” is always ryo, etc. However, for vocab, things are much less consistent.
For example, WK uses the mnemonic “shit” for shita in 下, 親しい, etc. but shito in 淑やか. Likewise, “hag” is used for both hage (激しい, 励ます), but also haga in 鋼.