That's crazy. Second time Facebook values some completely random app hardly nobody uses at such a high price. The last one was Snapchat. Never heard of either of these apps. I guess they have their own niche users and it's aparantly big enough for them to value it that high.
Seems to me coding a messaging app from scratch would cost way less than buying one though, but guess it's all the copyright/patent/IP stuff that they want, and guess the existing userbase too.
I'm still waiting for the day Google buys Facebook. G+ is a failure, so they can just buy Facebook and convert it to G+. I'm sure Google salivates at the thought of gathering, mining and selling all this data.