I feel for chargify in their need to update their pricing scheme. We are trying to do just that with one of our free products right now. Getting freemium price points can be tricky. It is easy to engage in some degree of wishful thinking in the value proposition of the paid offering to most users or to ignore the potential cost of acquiring a ton of free users and not enough paid users. Obviously these calculations can become easier if you can afford to launch with free and then add paid since you then have acquired a very valuable piece of information that can take some of the guesswork out of the value/feature equation – user feedback.