The first time I heard about Prison School was a very long time ago, and I thought I wasn't going to enjoy it, however, this anime proved to be more than I anticipated. I think most people would say that this anime is shit because it's ecchi, I thought the same thing before I watched it. In the begging of the anime, I was going to say it was "So bad, it's good", and while I still think that to some extent, after the ending, it proved to be better than I originally thought.
So in the end, should you watch Prison School?
My advice: Keep an open mind and watch the first 3 episodes, then see if you feel like continuing.
(I don't know if my english is good or not, so I'll apologize for any spelling mistakes in advance.)