So Wiz you want an extra guy on the jumpseat just to spot errors on every flight? If I've got augmenting guys I ask them to check the rest area and do the walkaround - and then stay out of the flightdeck until doors are closing.. Otherwise too many people on the 'deck
There are very specific SOPs for flightdeck prep and a 'helpful' extra can put a spanner in the workflow
If I'm the augmenting guy I stay away anyway 'til doors close....