The ephemeral photo sharing service handles messages slightly differently to Snapchat. To view an incoming image, you have to send an image back to the sender, without which you cannot view the message. Messages disappear shortly after they've been viewed, and are fully erased from Facebook's servers within a month even if they aren't.
However, users do not get a notification if someone takes a screenshot of the image they sent, a feature that is available in Snapchat. What Slingshot has, instead, is the ability to selectively send pictures to one, many or all contacts you've recently "slinged" with.
Sounds interesting? Head on over to the Play Store to give Slingshot a go, and let us know what you think.