Do you think Credit Karma is 'free'?
Do you think all those DNA registries are 'cheap'?
Do you think anything you do on Amazon/Netflix/Facebook/Twitter/Cellphone/Alexa isn't recorded, packaged, and sold?
"Big Brother With Benefits" is a perfect description of all these services.
Always be aware of what you're putting out there. Heck, Google basically steals anything you put on a crawlable Web page. It doesn't matter where it is on the Web, Silicon Valley will eventually get to it.
I remember a couple years ago while I was online dating that a couple of the sites were free. Both were fronts for subscription megalith Match.com. One of them was a blatant data-mining scheme and the other was designed to cast as wide of a net and get profiles of as many single people as they could, and probably was also data-mining. Not that I minded; I was deliberately vague about certain personal details I don't really want known, and I would rather part with non-identifiable data for a free service than pay money to let them do the same thing. (For the record, the sites didn't get me anywhere. Next time I feel like I'm ready to get back into dating, I am paying...just not for any site in the Match.com portfolio.)