I'm sure they work, but there is always a folder in my pocket. And 99% of the time it can be opened with one hand. In addition, there is a fixed blade, usually a cheap Mora in every vehicle and an inexpensive folding knife in the console. Those folders are primarily for my wife, she won't carry one, but is always asking to use mine. If I'm not in the car she has one in the console.
After a crash where I'm trying to self-extricate the knife in my pocket is the one that is most likely to still be where it was. I see the biggest benefit as a tool for those times I may need to extricate someone else. I'm sure it is a much safer way to cut a seatbelt than a standard knife.
Overall I like it and may get one. That, or something similar should be in every 1st responder vehicle