Hello Frank & All,
> One local manufacturer still uses these - another does not. Why were they
> abandoned by those who ceased to use them?
Many beekeepers thought the metal frame rests  could be a place for American
foulbrood spores.
>Do most folks use, or not use  them?
 When new they used the rests but on old equipment they were pried off and
the boxes scorched. It was cheaper to slip a 3 1/16 piece of wood back in an
fasten with nails than replace the metal rest.  One or the other needed to
be used.  I have however seen a number of Kelley boxes with the metal rest
removed and no piece of wood added in use in hobby beekeepers hives. Most
did not know what the problem was until I pointed it out.  They had been
cussing the maufacturer for cutting the box wrong.   As you correctly stated
only the metal frame rest intended for the box solves the problem if you do
not add the homemade wooden strip.
Sincerely,
Bob Harrison
Odessa, Missouri