What

Those indeed can be fun but be aware they're almost assuredly doing facial recognition on their users, and the whole system works by always retrieving the files themselves from a remote server, I'm fairly sure they don't even cache on your phone (I could be wrong there, though). It's really up to you if you think it's all fun enough and worth having fun socializing with your friends with the risk of lack of privacy in that respect. Maybe you can keep it to a minimum of anything important being talked about? Unless you have a major reason to worry about being targeted, most people can probably safely dip in just for a handful of throwaway conversations with friends.

Sorry other folk don't read modern slang.