I'm using Red Star Volume 6: Yakovlev's Piston-Engined Fighters as a reference to help answer your question.
1. The books are nicely paperbound, the pages are heavy of good quality.
2. Photos throughout, each page containing 1 - 3 photos each.
3. Every single type and sub-type of the Yak fighters development history is covered.
4. Limited combat use - front line information but there is information provided to highlight why the aircraft development evolution.
5. A chapter on foreign use is provided.
6. Color profiles for each aircraft type - sub-type is also provided.
If you are looking for a photo history - these are wonderful, many pictures are rarely seen.
If you want detail development history - these are some of the best in English
If you want Front Line use - combat history than you may be somewhat disappointed as front line use is not the focus of the book.
I strongly recommend the series as they provide information that unfortunately is lacking in English. They make a great lead in to understand the background for the aircraft.
The above information as far as the books focus is consistant for the Soviet WW2 aircraft. (the ones I have).
hope this helps