A couple of points on their Privacy page bothers me, though:
> Once you confirm your account, you may delete content you have posted at any time. <…>
> To sign up for Rooms, you may provide us with information such as an email address and usernames. <…>
> We may share information about you within the companies and services operated by Facebook to understand and improve our services [but the information from Rooms won't be posted to Facebook and vice-versa].
It'd be more fun if you couldn't delete your content (so that messages posted a while ago don't lose their context), but instead you could be absolutely anonymous (not even having to provide valid email address, which per above will quite likely be matched with your Facebook account at some point).