The USP: Gives you the chance to tell your friends (rather than strangers) that you want to sleep with them.
Pros: There is a strange thrill in being able to 'swipe' that acquaintance you've always fancied, asking them for a date (up) or telling them you want to sleep with them (down). Cons: It pulls in every single woman who happens to be your friend on Facebook, even if they haven't joined Down yet (your cowardly come on will be waiting for them if they ever do), making it rather pointless.
This hook up app for friends (and friends of friends) is the equivalent of passing 'I Like You' notes in class.
The USP: Hook up with the people you walk past on the street.
Whether it's matching you on your favourite interests or finding someone who you share mutual friends with.