So far, I'm using the book for hiragana and it's been a mixed bag. Some mnemonics are great. For example, for "na," there is a picture of a man holding a rope with a knot in it. Other mnemonics are a stretch, like the one for "chi," for which the author drew someone sneezing, with the explanation "AaaaCHIoooo!" In real life, no one says "AaaaCHIoooo" when he/she sneezes, and if anything, this so-called mnemonic would only confuse me by making me think the character is pronounced "chu" or "u." For the ones that are difficult to make a connection with the mnemonic, you simply have to make your own drawing or other connection, or simply memorize them.
I'll have to update after going through the katakana and kanji.