I read Sharon Salzberg's book on Metta meditation when it came out back in the 1990s. I see she has a number of books on the subject. Is it the case where you've read the first book, then you've read them all or are the others worth reading?
Are there any other high quality books on Metta meditation out there?
In reading the scriptures, there are two kinds of mistakes:
One mistake is to cling to the literal text and miss the inner principles.
The second mistake is to recognize the principles but not apply them to your own mind, so that you waste time and just make them into causes of entanglement.