Not a bad upgrade, but I can't see why you need the strap. Miata doors weigh 11 pounds and there is plenty to grab.
My guess is so whatever hardware he inserted in the hole that was there had a reason for being there. A random screw and washer on a door panel would look odd.
This. There's a big hole in the door panel there, and it flops around a bit if something isn't there holding it on.
The armrest will also be smaller and completely smooth, so there won't be anywhere to grab on that, and with the window closed there's nowhere else to grab.



