Facebook's Mark Zuckerberg spoke frankly on the subject of mobile app install ads during the company's first quarter earnings call, naming them "one of the most important new ad products" offered by the social network.

COO Sheryl Sandberg provided some numbers to support Zuckerberg's assertion.

She said 3,800 developers used the mobile app install ads to drive a total of 25 million downloads across both the App Store and Google Play.

Sandberg further stated that forty percent of the 100 top-grossing apps for Android and iPhone have advertised on Facebook.

Curving upwards

But, are the click-through rate high enough to justify the cost per impression?

Looking at the chart below, it's clear things are changing fast. 



The click-thru rate spiked dramatically between December 2012 and January 2013, but has since levelled off.

Meanwhile, with the market growing to include close to 4,000 developers, the CPM (cost per 1,000 impressions) has almost doubled in cost.

[Source: Inside Facebook]