I have a feeling that the rollover protection that pops up behind the rear seats were designed for a "paved/solid" surface. The tops of the posts are so wedge shaped, that if you rolled onto a grass or dirt surface, they'd probably just dig down into the ground; I'm not sure how effective they'd be in that case. If you stay on solid ground, they look to be structurally sound and would protect passengers effectively.
I say this because my brother-in-law flipped a Toyota 4-runner while driving down the highway a few years back. When the roof hit the ground, the sunroof broke and left a perfect outline of the sunroof. Where the side of the car hit the grass surface (the vehicle rolled off the road and onto the grass median) the side mirror left a perfect "hole" in the ground in the shape of the mirror.
I'll bet the two roll protections do the same thing in softer ground. There is a whole lot of weight on those two little wedges...