It seems to be similar to the rail-brake on streetcars...

I have to say I'm more impressed with the 'belt bag'... I'm fairly tall (6'3") and my wife is short (5'2"ish) so we fall on either side of the reasonable range of a seat belt; if she were wearing a seatbelt in a wreck at speed she would very likely break her clavicle and/or crush her larynx neither of which is a good outcome... in most cars I'm so wedged in it doesn't make much difference, though I do have some concerns about my size and air bags (I'm losing weight and am down to about 250lbs (from 270), will probably get down to somewhere between 220 and 240 depending on muscle mass and conviction).

I do like the braking bag, especially as it lifts the front end which will help prevent you going under the lifted pick-up truck you're about to try to violate newtonian physics with.

Two questions though... Is it a one time use then pay $20 kagillion to replace or can it be reset? What kind of damage does it do to the road surface?

all MBZ safety features are 'throw the car away after use' type.