If using two servos on one critical flight control, via a matchbox, it can be argued that it is better to feed one servo DIRECT from the receiver and trim the other or others via the Matchbox. Thus if the Matchbox should fail, then one servo remains operational.

Having said that, I have never had a Matchbox fail, however, the possibility exists so routeing BOTH servos via Matchbox does not seem to be good practice.
Regards,
David Gladwin