When FB bought Whatsapp, Whatsapp was handling 20 billion messages a day and was the #1 app on the phone pretty much anywhere in the world, except for US, China, and Australia (it still is). Not that they needed some tool to find that out.

FB did an amazing job in keeping their acquisitions fairly independent and let them keep grow. That's something really hard to do and they deserve credit for that.

It is easy to buy the #1 messaging app in the world, if you have the money. It is hard to make sure those people still stay motivated after the acquisition.