I'd like to cover a few issues in this thread.

First of all, like some of the other folks here who were/are first responders, we prefer crashes with people in seatbelts, because that usually means extrication, not recovery.

To address some other points:

Jamming: seatbelts come in a range of engineering concepts, all share some sort of intertial sensing that locks the belt on impact (it's a pawl on a ratchet sort of assembly) and the force of impact can cause deformation in the structure of the belt latch, so that's why they sometimes jam.

Airbag seatbelts: all airbag systems deflate moments after deployment. in the case of the ford seatbelt airbags, the same concept applies. the entire belt is not an airbag, so there are cut points for ordinary tools (I used Medic shears almost exclusively to cut seatbelts on extrications. Medic shears are advanced alien technology).

Fixed (racing) vs. adjustable: a 5+ point harness is a great thing - IF you are a baby in a car seat, with your own personal roll cage. For normal adult drivers, the 3 point harness method is the only realistic method when you have no idea of size and shape of the people who will be driving a vehicle.

Finally...very few crashes result in fire, and not that many crashes are into water. I don't suggest NOT being able to self-extricate from a stuck belt, but it's not a scenario that is all that common. A Res-q-me tool or a lifehammer is a perfectly good tool - don't hang it from your rear-view mirror (I see that a LOT)if you intend to actually be able to find it after a wreck. It needs to be affixed somewhere in the vehicle.