Shiwasu no okina can generally be trusted to write hot characters in his manga, and I would lean on the side of this manga being no exception.
The main appeal of this manga is the thrill of not getting caught having sex in a library. This motif is solid and well-executed and the tension builds up through the whole story.
The characters' behaviour is a little bit childish in the beggining, which might be off-putting for some, but there's either some healthy character development (if you may call it that) or just the snowball effect of having to get more perverted as the story goes on.