I never used SteemPress, but was considering it. Thank you for your warning!
It is one thing to clearly state that they were taking a cut. After all, they created a service and I understand that they would want to be paid for their hard work. If this was stated this information up front, the user could make the decision whether that cut was fair or not and use/not use the service because of that.
But being underhanded and secretive about it? That is unacceptable.