Paid software absolutely has a place in the world. Evil companies producing evil software designed to build a monopoly and lock out FOSS apps do not. I don't think Sync falls into the latter and I'm happy they've made the choice to be able to eat.
Just commenting this for those that may think free software is referring to price.
Free software is diametrically opposed to proprietary software, and not paid software.
Free software is free in terms of libre, not necessarily gratis. And there are corporations and individual contributors to free software that do charge for their product and maintenance of it.