Ok, according to the FAA there's ~3,739 U.S. registered passenger jets which carry more than 90 passengers (http://atwonline.com/aircraft-amp-engines/faa-us-commercial-aircraft-fleet-shrank-2011). Cost to fit just U.S. registered aircraft with this device would therefore be just under $374 million.
Number of U.S. registered passenger jets which can carry > 90 passengers that have crashed with any fatalities since 2000 is maybe 5 (https://en.wikipedia.org/wiki/List_of_accidents_and_incidents_involving_commercial_aircraft#2000), and the number of those where it wasn't immediately obvious where the wreckage was was zero.
So in the US alone, we're talking close to $374 million dollars to fit out just aircraft that carry more than 90 people, for a return of nothing. I couldn't find a reliable estimate of the number of commercial passenger aircraft currently flying and capable of carrying > 90 passengers globally, but I did see a number of guestimates in the 15,000-20,000 range. Assuming there's only 10,000 currently active passenger planes in the world capable of carrying >90, that's $1,000,000,000 to fit them with this gadget. The number of planes since 2000 which went down with passengers on board which couldn't be immediately located is what? Two? The Malaysian Airlines one now and the Air France one a few years back?
So if every passenger plane in the world capable of carrying more than 90 people had been fitted with this gadget since 2000 we'd currently be running at half a billion dollars per actual use. I can think of a *lot* of uses for half a billion dollars which would actually save tens of thousands of lives. There isn't a single case in the last 20 years where this gadget would have saved a single life - all it can do, at best, is provide slightly faster confirmation to grieving families that their loved ones were indeed dead and here's how it happened. Which is not trivial - I don't mean to invalidate what such news might mean to someone with a loved one who was on that flight - but oh, my, that's a staggering bill to just provide speedy confirmation of a loved one's death for a few hundred people.