Both series feature dirty jokes and randomness (Nupu Nupu is probably more random). Nupu Nupu actually features similar plot to God Save the Sugekoma-kun! in later volumes (as one of many subplots). You see in God Save the Sugekoma-kun! we have a perverted student targeting his teacher, but in Let's Nupu Nupu it's the other way around. If you found either of those series funny, you're ought to read the other one too.