They are popular novels (流行小说), as opposed to literature. So they are easy handy material for the intermediate to advanced learners to get used to reading on English. I would not say they are.good educational material for learners. I would say that they would not do any harm. "Airport novels" are exactly what they are. They are written for readers who wish to switch off their minds. Most of the people I know, for example, do not read Sidney Sheldon, and would apologetic about it if they were caught reading one on the plane.