It's extremely up-front, the home page is offers for credit cards and loans and such. It's also explained here: https://www.creditkarma.com/faq/howitworks

In several years of using it, they've never emailed me advertising anything, and while they're obviously sharing my info with credit card companies and banks, I haven't gotten any marketing from them either. If you don't care about the recommendations, as I don't, you can use it for your taxes and never think about it the rest of the year.