When I was 'in the business' we did not even monitor 121.5, let alone transmit on it.....
We had no capacity to do so - except on one very rare occasion in Derby during a "Kangaroo '83" military exercise when we were 'loaned' a portable "Bayside" VHF transceiver for the purposes of the exercise.
(And we actually used it to contact an aircraft which had otherwise 'nil contact'.)
I don't think that there has been any 'change' since......
Cheers
