When a vehicle is in a collision, especially a roll over, any thing loose will fly all over the place, If your cutter is loose in a door pocket or dash compartment, clipped to a visor or seat belt before the collision, it won't be there after the collision. If it is your glove box and you need it, you won't be able to reach it if the seat belt is stuck.
A dedicated seat belt cutter is preferable to a knife. Seat belt cutters have their cutting edges on the INSIDE of a curved sharp edge. No point to jab your belly as you try to cut the belt.
Paranoia is your friend. If you have only one seat belt cutter in your vehicle, secured in the driver door pocket, and you are incapacitated, your passenger, if you have one, won't be able to reach it. So always have two. A third one or two in the back seat if you are a really paranoid preparedness freak.
The best place to secure it is in the center console of your vehicle, if there is one. 2 reasons - First, it's possible that a door pocket might be inaccessible in the event of a T-bone collision. The second - Passenger or driver can reach into the console compartment easily. If there is no center console, you can use a door pocket. You just have to secure it properly. I have one in BOTH door pockets of the truck (no center console) in the event my passenger has to use it.
For my cars, I secure mine in the center consoles. For the securing, I used a long strip of 2" wide velcro.
First, I superglued a piece of velcro to either side of the seat belt cutters.
Then I glued one long side of the velcro to the inside wall of the center console. Actually I did this twice - a cutter on both sides of the center console so both people in the front can access a cutter if time is short for evacuation of the compartment.
Then I stuck the cutter to the velcro.
I sewed a piece of scrap leather to the other half of the long piece of velcro to have a large "pull tab".
Then I stuck the other long velcro half to the cutter and pressed the tails down firmly on the two "tails" of the velcro sticking out either side of the cutter. This way if you have to pull the tab, the knife either sticks to the piece you pull of or it stays stuck to the part glued in. Either way, you have a cutter.
All this ensures that the cutter will be exactly where it should be in the event of a collision. Easy to find, even in the dark. If the vehicle is inverted, when you open the console, the cutter won't fall out and get lost. If it weren't secured, it could just fall out or be buried under all the crap that accumulated in the console an hard to find even if not inverted.
For the door pockets, you do the same, just mount it where ever a large flat spot is available.
