As usual with a book written by a man, I rely on him mainly for background: history, geography, and social and religious customs. He does have some peculiar beliefs, such as the absolute conviction that Jesus was born on December 25, but the information he gives on the Jewish lifestyle totally outweighs such problems. Keep your eyes open and you will be fine using it. Just being able to put these people in the context of their beliefs and customs has changed completely how I view some of the events of the gospels. I feel like I really comprehend what was happening—the tension and even danger in the air at times.
One caveat: this book was written in the 19th century so the language can be daunting. Sometimes you will read several long, almost tedious, paragraphs to get to a nugget of gold, but it is worth it. In the back of the book is a scripture index. Rather than having to wade through interminable text, simply look up the passage you are interested in and you will find the page(s) you need to read.
This book is considered such a classic that even more than 100 years later, you will find reprints. (Of course, this also means that some of the material is dated. You might want to read it alongside a more recent volume, e.g., Tenney’s New Testament Times or even more recent, Ferguson's Backgrounds of Early Christianity, to make sure that later archaeological discoveries have not changed scholars’ understanding of a certain custom.) The latest reprint, a big blue one-volume affair, unfortunately has several typos in it. However, I have never had any problem figuring out what it was supposed to say, and occasionally, after a long period of hard study, you will find some comic relief. Take for example, the mention of Martha in Luke 10, preparing for the visit of the “Great Rabbit.” Someone relied a little too much on their Spell Check!
I also have three other of Edersheim’s works which I use not as often, but enough to justify their expense: The Temple: Its Ministry and Service; Sketches of Jewish Social Life; and Old Testament History. All of these books can be found on Amazon.com for as little as $7 each, depending upon how much you care to spend and the condition of the book. Christian Book Distributors (if you are a member) has the four-pack for a reduced price. It is worth the membership dues. In fact, I pay the membership price and then order for friends, which is perfectly acceptable.
Two other Edersheim books I do not have, but have just recently heard of are Prophecy and History in Relation to the Messiah, and History of the Jewish Nation After the Destruction of the Temple Under Titus. Since I have never used them I cannot give a recommendation, but based upon my experiences with the others, they might be worth checking out.