If you know Haynes manuals, you know what you are getting. This is typical of their offerings. I am in the process of rebuilding my Healey. I own this book, the Autobook manual and the green cover official factory manual. Of the three, if I had to choose the one to be without, it would be this one.
The images are frequently the least helpful. The other books commonly have drawn images. This one relies on photos. Unfortunately they are black and white and often too dark to get full detail. In most cases, I much prefer exploded diagrams so I can see how things go back together.
The physical book is the lowest quality as well. Obviously a paperback is a paperback, but this is still not as robust as the others.
Although each of the three has some items the others do not, I recall very few novel ideas I got from examining this book. In my mind this book is best for focusing after I have examined the others to figure out how things are done. Helpful, but not essential.
All that said, If all you are going to do is tune ups and basic maintenance, this book might be enough. For a comprehensive repair or rebuild, you will need more than this delivers.