Sometime ago I listened to a radio documentary where a marketing company figured out the optimum length of time to offer a product as a free trial. In this case, "optimum" meant 'long enough that the consumer felt they could buy risk free but also long enough that the likely hood of the consumer being willing to return the product, was greatly increased."

My opinion is that a stated "break in period" is designed to serve much the same purpose. Eventually, you get used to them and the thought of going through a return cycle starts to feel less inviting.

Trial periods, however, are great especially for the consumer in this new online purchase world. One just has to enter the transaction being mentally prepared to take advantage of it if you don't get exactly what you expected.

By the way, this radio documentary is a weekly show on CBC radio that talks about marketing. It is quiet aptly named "Under the Influence."
With great power comes Awesome irresponsibility.