If you read an older version of this book, then you have missed a little something. Many of the words were cut out of the book before it was published. Moreover, due to contractual agreements the missing part of the book could not be printed while Robert A. Heinlein was alive. Now dead the missing pages have been restored to many versions.
Now all bets are off. So count the words in the copy you are about to buy and be sure you have the whole thing. And for those people who read the original release I suggest you re-read to see what you missed
If you have not read other Heinlein books then you may not realize how his writing stile has changed over his life time. This book is more of a latter Heinlein style. Some people like both early and late Hein lend others prefer one or the other.
The audio versions have all the pluses and minuses of audio. So you will also want a copy of the book for reference.