Warmly recommended in small daily doses, the way most improvements are wont to happen.
If anything, it's better to start the book with an open mind. This one relies strongly on mnemotechniques, connections to things one already remembers. Since everyone's memories are not only personal, but regarded through a unique cultural perspective, it is not hard imagine why some steps might not go as smoothly as others.
Actually, most are likely to encounter one or more points where the author's suggestions are bound to outright clash with the reader's own way of remembering ("which has worked just fine so far, thank you very much".) In my case, that is anything number-related. I remember numbers by assigning personalities to the primes and letting multiplication do it for the others (0 is the apathetic assassin, obviously) Thus, thinking about 16 as Arnold Schwartzeneger flexing is not going to work for me, when 16 is clearly a very baroque, younger Aunt Petunia, doing pirouettes, if anything.
There's no denying, though, that the guy has the right of what he's teaching, so the point would be to go one step further and personalize the principles to find a method that sticks with the way each reader is wired.