A Mini with a 'Multipoint' cage, bucket seats and harnesses fitted with the correct cage padding, will kill you because you drive on the road? But not when you are driving at 90mph though a forrest on gravel in close proximity to trees, many of which can be imovable?
It wont kill you at 90mph in a forrest on gravle with tree's because, you are wearing all the protection gear, with a proper race seat with braces at the side by your head, and a full 6 point race harness, which stops your moving arround.
The cage protects you from the initial impact/s
The cage padding and helmet protects you from the cage.
In my opinion, a roll cage is just that, a
ROLLcage. It protects you incase of a roll over!!
its only of any extra use if you have the full cage, with side impact bars.
all of this will protect you in a crash from the impacts. but you have to remember what is protecting you when you hit the cage!!!
IF i ever got a cage, i would wear a helmet while driving the car, and have all the padding in nesercery places.