What do you guys think about this?
It's nah for me. Waste of phone's energy and battery life span.
Pi doesn't use your battery or any energy. Only you have to click a button in 24 hours. You can check if your mobile is switched off, pi will be mining, because it doesn't use battery or CPU. I have been mining for 8 months but I don't remember that pi has done anything to mobile. So I think it's safe.