SlideCoin is a highly legit way to mine bitcoin through ads from my test and views.
I'm using an Android so I got the app from play store which you can also do that but I don't know if the app is available for IOS but you can do your research on that.
The app mine bitcoin by using the spare processing power of your device. I won't go into detail about how that works here if you are curious read the wikipedia article.
So your phone is doing work that earns you money, the app just does it in a way that doesn't influence you noticeably and the referral system works by getting more people to mine thus making the developers more Bitcoin which they can use to pay more people and the reason they keep the screensaver on is because android pauses processes when the screen is locked which would stop the mining process.
Here are some proofs that the app works, I have mine too.
There's no harm in trying it, you can earn more by using the app as your default messaging app.
USE yah198 as your refferal code, also visit here to join the affiliate program.