It's a great book. I keep a copy in my scram-bag, as it's the kind of knowledge that could be the difference between life and death, one day.
If you're going to rely on stuff like that, its best to commit to knowledge and practice.
It's mostly handy for "was it the one with the serrated leaves, or the one with the smooth leaves which is toxic?".
I've been foraging for 25 years so that knowledge is sort of built in (at least in the UK) but I still won't touch mushrooms!