FWIW:
I can confirm having used FT_VERSION in the past. I briefly had one agent where we tried the old protocol for a while due to semi-regular crashes during file transfers.
However, I have also repeatedly been warned against using FT protocol 1. It has been mentioned in each and every "Automic Health Check" even when I had just the "host characteristic" defined and didn't have it assigned to any agents anymore.
Automic seems to be rather strongly of the opinion that the old protocol should not be used, let alone not be used as the default for entire installations.
Hth,