It needs to be located where you can find it by touch, don't count on being able to see it if/when you do need it. As for one on the passenger side, only if you expect that person to be able to react correctly and know how to use it. I wouldn't spend the $$ on more than one; although it might be good to have a spare if you happen upon an accident and need to get somebody out of their car.

One on your seatbelt so you can follow the belt to the tool in the dark, and a spare in the ashtray (assuming you don't smoke) or in the console where I keep my emergency cutters.
_________________________
Better is the Enemy of Good Enough.
Okay, what’s your point??