I dropped my phone for the first time onto a wood floor with this case on. I think it hit the floor on the side with a soft thud. The way it feels, I guess protection on all sides other than the front is excellent: you get leather on the outside, plastic in the middle, and soft cloth on the inside, all of which would absorb the energy and distribute the shock to a larger area. From what I have seen of a YouTube video drop testing of the iPhone with a bumper from various heights and how well the phone fared, I think back and side protection of this case is more than sufficient.
What about the front drop? Unless you manage to drop you phone so that it lands flat with the face down, the side protection is going to take care of the impact. Now if you manage to do that, there is a thin raised lip that will take away probably most if not all of the impact, unless you hit a raise surface such as a rock, in which case no case short of something with thick screen protection is going to help if any.
So let's assume that the front face flat drop is the most damaging drop. What is the probability of that happening? I am talking about a drop where the face of the phone lands flat on the ground. Let's start with the chance that you drop the phone over the years that you care, say 2 years. My records so far is 1, but let's make it 5. Chances are you drop it while holding it some what vertical, so of the 5 times you drop it, what's the chance of it falling flat on its face? The odd is slim to none. Now, add to that very slim chance the protection you have with a slightly raised lip of the case. I think your odds are pretty good.
Now let's look at the big picture. I could get a more protective case which would get in the way of my daily enjoyment of the phone because the thick raised lip and screen protector, or I can choose a case like this with a minimal raised lip which doesn't hinder my access to the edge of the screen (the reason I returned the Incase Slider), yet according my estimate provide sufficient protection. I think I'll take my chance.
But then I am one who got this case primarily for the way it makes the phone feel in my hand. I love the way the phone looks and would have used it without a case (tried that for a month) had the edges been rounder.