This answer might be premature, since my group graduates at the end of this month, but since no one from the first group has chimed in I hope you don't mind if I do.
The program is not easy but if you are up for learning how to write better online, and get your content found on the internet, it has been great. Personally I have learned so many things from HP that I really had no idea about.
You also get grouped with a couple of dozen other writers and friendships build quickly.
My advice to anyone who gets invited is to accept the invitation. The knowledge that you gain is unreal and incredibly valuable to anyone wanting to be successful writing online.