I have more than 50 Osprey books in my collection. Many are written by some of the best authors in the business, such as Thomas Jentz, Hilary Doyle and of course, the honorable Steven Zaloga.
They are a good value for the money, are generally accurate, give a good overview of the subject and they have excellent line drawings. I like them.
The "How to" series of modeling manuals however, leave something to be desired, They are not the "Complete How-to manual" for whatever it is you are building, more just a general outline and some nice photos. Useful, but they could be better.