Yeah, Facebook does make it quite safe. Personally, and I know that this is a bit silly, but the thought of all my actual Facebook friends seeing that I have signed up to this put me off at first. Then I was like "fuck it, I'm curious!" - but it doesn't mean that others will come to the same conclusion. It's similar to announcing on Facebook that you've just signed up to a dating site. Lots of people do it these days, even talk about it quite a lot, but it's not something you'd make a status update about.