No problems experienced to date when using a one way Hitec trainer cord #58310.
However, good practice to remove crystal or module from buddy box to prevent any spurious RF transmissons if by chance a two way Futaba cord is used. (This is now essential if using a Futaba 9c as master becuase you wil then have to use the new Futaba square ended trainer cord.) First issue Futaba 8UAP occassionaly let out a little smoke when a choke on the trainer board overheated if anyone turned on the buddy box - have not heard of that happening for awhile.)
FWIW, I now regularily use an Eclipse with a Futaba 4VF as a buddy box for newbies and a Flash 5X on mode 1 to buddy a Futaba 9c on mode 2. (module out of 9C and no way does he touch his on/off switch when the trainer cord is attached) With all computer TX the battery must be left in place and it powers up the LCD and appropriate part of the trims etc once the buddy lead is inserted )
regards

Alan T.