Can a tempered glass screen protector protect iphone 6 from face-first drops?

I already have a Thule Atmos X3 phone case which is made of polycarbonate and silicone, and is supposed to be able to protect the iphone from drops up to 6.6ft and is supposed to be very good at this.
However, it doesn't come with a screen protector.

Could a screen protector prevent my iphone screen from shattering if it falls face-first from a few feet if the screen protector takes the damage and not the actual iphone screen?

It can. It depends on the amount of energy imparted.

You have to understand the physics of it. When your drop something it has kinetic energy. As it falls it collects more and more until it reaches terminal velocity. When it impacts, the part that impacts obsorbs the energy until it reaches a breaking point and then shatters. So if you put a tempered glass cover on your phone and the amount of energy that is imparted from the fall is less than the energy that it takes to break, it won't shatter. If it does shatter and the amount of energy remaining is less than the amount it takes to shatter the screen, your cover will shatter but not your screen. So there are a lot of variables there. And To Improve App lock Security, You must also install Leo Privacy Guard in your smart phone, with Stylish themes.