I had a friend in that class that complained about the low averages, and I looked over their exams and they were much harder. Hardingers averages are usually around 70-75%, whereas that classes was in the 50-60%.
You only get 6 weeks in the summer so you need to be ready to spend ALOT of time studying, im talking about no going out on the weekends at all and spending 5+ hours studying on your own a day.
Whats good about the summer is that it is your only class so you can focus on it, but I would not say that it is easier to take a class in the summer.