Many useful procedures explained and taught: 2-column addition, left-to-right subtraction, direct multiplication by numbers greater than 12, mental division of large numbers, more. Also numerous helpful shortcuts. More than 8,000 problems, with solutions.
While the book is old, it is still adequate for what it sets out to do. How to Calculate Quickly does a good job of listing problems to solve, but beyond that, there isn’t much to this book. It intends to teach a number sense. If you put in the time, you will certainly reach that point.
I really like this book. It kind of reminds me of the Hanon piano exercises, but for arithmetic. I think it provides good practice for the art of calculation, but what I like most about the book is creating my own little exercises off of the exercises directly given in the book. I almost look at it as improvisational. Exercise #2 is one of my favorites. You have a table of numbers ranged out-of-order from 1-100, and you add 11 to each number. It's like 1 -> 10 -> 11. You first add 10, then 1. I call these number pivots. It's kind of the foundation for a more rhythmic way of approaching it for me. I think it provides good practice to get started, but then you can create your own little exercises off of these to gain more of an intuition into it. Like, for example, I'm next adding n! exercises, along with other movements. You start with the book and then you can improvise off of it.
Cut out the exercises and you've got a five page pamphlet on arithmetic. Those five pages would be pretty interesting, though, with history and commentary about the art of calculation as well as an introduction into old methods that people used to use to do rapid mental calculation.
The exercises provide the bulk of the value of this book. I'd recommend setting up some tables in Excel in order to help facilitate your practice.
All-in-all, not bad, but it certainly won't change your life.