RE: PCM?
Per Futaba, the recovery from an interference event is on the order of 20-50 milliseconds. Damn fast. For example, suppose the signal is lost for 250 milliseconds, or 1/4 second. The pilot will not have control for 1/4 second, plus another 20-50 milliseconds, or a total of about 300 milliseconds. Basically, not much more than a 1/4 of a second. You won't be able to measure the lag time without a scope attached, and it would be invisible to the pilot. The recovery time on JR is roughly the same.
You can advise the person in the shop that he was incorrect, and have them check with Futaba for verification.