When its "free" you pay with your data !
There are only a few code files. You can make sure that only the root domains are sent, without parameters or end pages. I mean, you can make sure if you want, I haven't done this yet, maybe over the weekend, I just looked at the repository on github. Thus, all the data you provide is traffic statistics. You can choose trusted vendors, and if you also constantly use a VPN, then the data will be depersonalized as much as possible.