Dated, but useful resource for a biblical understanding of angels and demons.
The challenge with any book on angels and demons is the lack of Biblical information. This eventually leads to other sources of our information to answer our nagging questions. This book does its best to avoid this trap but still falls in it from time to time. The book is well organized into small chapters and is probably more useful as a reference instead of being read cover to cover. I read it cover to cover, but found it often repetitive and it took some logical leaps at points.
Some OT appearances of Christ are interpreted as angels in this work, which affects some of his conclusions. But if you don't affirm Christophanies in the OT, like in Daniel 10, then you will be fine.
His conclusions on the possibility of demonic possession for Christians will probably rub some the wrong way. While I did not agree with his conclusion, I did have to admit that it was Biblical founded and appears to be a valid option.
One of the big cons is that this book shows its age when it references occult and demonic possession. It was originally written in the '70s and that comes through in this part of the book. Much of the conclusions around demonic possession and how to deal with it are taken from experience instead of only Scripture. There is also little interaction with historical Christian thought or even other theologians. This weakens the argument significantly in places.
Should you read this book? Probably if you are interested in learning more about what the Bible says about angels and demons. I honestly do not know of many resources that touch on this topic at all without going off the rails. I think it is a useful, but flawed book. The lack of other alternatives makes this the best option in my mind.