With its largely product-specific focus (Tradestation 6, early 2000s) this book comes across a bit dated. While much of the general Tradestation and EasyLanguage concepts and references are still applicable to more current versions of the product, much of this material has been freely available on Tradestation.com. IMHO, the main value of this book is in chapter 5, about "Measuring Trading System Performance and System Optimization". Again, concrete product references are outdated, but the concepts elaborated are timeless and very relevant (e.g. how to measure consistency of any trade strategy/system)
If you want to create your own indicators for data analysis & programming is not your thing then Easylanguage programming lang is for you. Tradestation started using extensively, later Multicharts adopted it (I use multicharts since it allows third party data feed easily & lot more user friendly) This book will surely help you at initial stage. There are few interesting indicators author coded & added for readers as extra bonus. You can backtest & use if you like.
I wanted a book to learn Tradestation and I was a bit disappointed with this one. The first 25-30% of the book teaches the basics of tradestation and its development IDE. However, there is some good information on building algorithmic trading systems later on.