The letter was interpreted as, "Hey, we're running late, sorry. Oh yeah, we're also charging for the sleep report separately now; so, we'll make up for the delay by throwing in some free months that you already were planning on getting and then charging you for the latter months you also thought would be free. You're welcome!"
People felt duped, it's not about the dollar amount it's about trust. WakeMate have since clarified that basic reporting will remain free.