I find 99% of the mnemonics made by others to be worthless. For the mnemonics I make myself, that ratio improves to be maybe only 90% worthless. Most recently I have been shocked at words that I have forgotten despite having created what I thought were incredibly clever mnemonics. I think the best mnemonics are the ones that are based on a visual image that resembles the character, and is in some way absurd / outrageous. I noticed that a lot of users create mnemonics based on radicals, but since I never properly learned them or even tried to study them systematically that doesn’t work for me.
I really wonder if it works for the majority of the authors. An effective mnemonic really exists in one’s head, so to write it down is only to document it. When I have to click on “mnemonic” I am really just soliciting a hint. Still, I feel somewhat less humiliated when I can write the character after reading the mnemonic / hint, after being stumped by the prompt. I guess we are also training ourselves to memorize mnemonics? sigh