What on earth is a 'gadget'? What about bicycles? Sewing machines? Watches? Pocket barometers? SEI spotmeters? Micrometers? Screw cutting lathes? Of if you want 'em small, watchmakers' lathes.
Also, what is the
purpose of a gadget? To show how clever and cool you are? To show off what you can afford? Or to do a job, usually better than the alternatives?
If sheer mechanical genius is what you're after, the Antikythera Device --
http://www.mlahanas.de/Greeks/Kythera.htm -- is a strong contender. Sure, the M3s I've owned and handled have been the smoothest, mechanically sweetest Leicas I've ever encountered. Buying an M3 as a gadget is however quite different from buying a camera to use, which is why I currently have M2, M4-P and MP film Leicas, and no M3 (I sold my last one many years ago). I suggest that
if you know what it's for and how to use it, an M3 also differs from a gadget, because a tool is only a 'gadget' in the eyes of someone who doesn't really understand what it is or how to use it.
Cheers,
R.