I believe the capsule was designed to exist in both Stable I and Stable II situations. Although since Stable II is obviously a lot less desirable they have a system of uprighting bags which can flip the capsule over, only they didn't completely inflate (probably) due to a short. They're working on it. As tests go, i'm pretty sure they found out what they needed to find out.
The difference between this an Mercury is that this doesn't have an explosive hatch. For simplicity's sake they basically bolted on the hatch as many times as they could. In fact, i think it can only be opened from the outside. This is liable to change in future iterations though (as in, the iterations that might eventually carry a person). You can
read up on the hatch design, it was largely crowd sourced. Come to think of it, if you have a legitimate concern/suggestions for improvement then post them in the comments, Kristian often replies.