This is a really good example of how to write ensemble music and put it together with a convincing playalong CD. The pieces could be described as easy-listening with the parts mostly in rhythmic unison. The harmonies together with the jazz combo are quite lush (although there is some unison playing) and you can hear all the jazz-style articulation very clearly. Although there are only 4 quartets each one is substantial for this idiom and your investment here would be quite justifiable. My only gripe would be that Cool Tune and Waltz for Four are in 4 flats - but you can't have everything!
Form a fantastic, swinging quartet with three colleagues playing the same instrument! Or you may choose to use another Jazz Quartet book to form a combination and play together with other woodwind instruments, such as the saxophone, flute or clarinet. This will make the music sound really jazzy.
Difficulty level, roughly compared to ABRSM exam grades. 0 is total beginner, 9 is advanced (beyond grade 8).