There is no need to convince people to buy it. The central server needs some funding but only minimal.

However, one workable way to sell it is to make the product free, and then charge a fee — very clearly explained up front — when a restore is needed.

You can also pre-sell the restore fee, at a discount to paying it at restore time. Ie. “You can buy the product now including the restore tools and service for $30 or pay $60 when you need to restore.”

However, I was expecting this philosophy might eventually be adopted by an open source tool. For one thing, you want the comfort of knowing that you can see the source code of a tool that is going to store you most precious data on other people’s machines (friends or otherwise.)