David came across an app called Clean Master that's supposed to protect and optimize your mobile device. Leo isn't so sure. He's not really impressed with download numbers, either. It's whether the app really works. And even if it does, it's unnecessary. David doesn't really need it. It's not doing anything important and some of the things it does is bad. It can certainly kill his battery life. It will also delete temporary files that will just cause his phone to download them again when he returns to that site. So it's not really doing anything. He's better off just keeping his OS up to date.