As an outsider
OK I'm no ATCO (Did try once) - There's an engineering principle at stake here - Often the simplist technology works well in unforseen circumstances - simple to use for both parties espcially under duress. - Keep those "Bean counters" away from your VDF sets & Ariels. Yes I have seen it in action.-
The technology is old, but forms a tool in the armoury that might be needed by a controller..
Sorry to intrude.
CAT III