There are 2 ways to learn Colregs. One is the rule and the reasons for the rule, light shape etc. - rather a classic intellectual approach to learning a body of work in its context. The other is a practical approach of repetition and natural progression groupinging similar topics.
This book uses the latter. With concentrated effort I was able to master all the previously difficult lights and shapes. I particularly liked the organization which does not simply follow the stucture of the Colregs, but still has a good cross reference for when you want to check what the rule actually says.
Essential for learning Colregs in a 'bootstrap' manner. Essential for RYA courses.