And the RAF VC10s and C130ks still have it! One problem with the iso-echo function is that if it is left on and you fly into a very active cell, all you will see is a thin green line with a big black space behind it leading you to believe that all is well if you've forgotten you're in iso-echo mode. An Israli Airforce Herc broke up over Belgium many years ago. The iso-echo switch was found on in the wreckage leading the investigators to believe this is what happened.
I adopted the policy of never taking my hand off the switch if using it.