These are 4 novellas that did not fit into his "future history": Most were written in the 40s and 50s. Two originally came out under pseudonyms. These stories are more like his later work, if you like that, you'll like this. They are not like his future histories very much.
Reviews of this book are very mixed, depending upon which type of Heinlein one prefers. This book has been reprinted many times, sometimes as book 1 and 2, with two stories in each, sometimes as one book. This is the one book version. Since it first came out in 1957 and was last reprinted in 2000, and you care, you should pm first to find out which year the book came out.