Not a bad spot unless you ever have a passenger sitting behind you. If that's a possibility then I'd flip the fire extinguisher bracket 180-degrees so instead of lifting up on the release clips you have to push down. That would also put the fire extinguisher content-release lever on top rather than the bottom. The narrator keeps saying there's plenty of room for a passengers feet but I see a problem with their feet hitting and releasing either the bracket release clips or activating the fire extinguisher by moving their feet.
In my previous '69 Dart I had one mounted on the transmission hump in front of my floor shifter (I had a bench seat in that car). I haven't yet decided where one is going in my current Dart build when complete, but there will be one somewhere.