Everyone familiar with WordPress knows the tactic of giving away free themes in order to build a name or attract customers to your paid offerings.
It’s pretty much a win-win for everyone. If you’re happy with the free theme, then carry on with it. It you want more functionality (or support in many case), then you’ll need to upgrade to a paid option.
At the very least, free themes let you check out a designer’s work from the inside with zero pressure involved. And so all in all, free themes from professional theme developers are a good thing.