The mountains listed in this book have become known as the "Welsh Nuttalls," indicating the success of the book more easily than anything else can. The Welsh Nuttalls are summits at least 610 m high with at least 15 m descent from them in all directions. (That's 2000 ft, 50 ft, for the SI challenged.)
I've hiked all of them, many of them multiple times, using this book as my guide. It's a durable little book with a plasticised waterproof cover, suitable for taking on the hill, and I found it useful to do so on some occassions. (It's no substitute for a proper contour map, of course.) The sketch maps are useful and the line drawings pretty. The suggested routes cover all the summits once only and form a loop to finish at the same place they start, which has (sometimes very limited) car parking.
These constraints make some of the walks inelegant and those with opportunity could do better by using public transport or leaving a car at each end of a linear hike - not that public transport is an easy option in most cases - or accept some repeats of summits. A determined person could tick all the summits in a year at one walk per weekend using this book - and have three weeks to spare!
Flagon says, roar! You might even meet a Dragon! If you do, be friendly!