Mechanics in the Jumpseat??? Not unless required to perform some maintenance function....(Common during Round motor days, to parallel generators or observe pilot reported vibrations) I know, because I was a mech and did it. These days, such cases are rare, and therefore a jumpseating mech is not needed. I used to fly a lot of MAC trips around the world, and we carried a mech because of the far off and funky places we went. Mostly they ate a lot of the catering, and slept. When not sleeping, they sat with their dirty boots up propped up on a sidewall, and smoked. When the A/C did have a mx issue, they complained of no parts(true) and would simply DMI the problem, if possible. Hell I could have done that. When the A/C broke hard, It was usually beyond the capabilities of one mech. So if a mech needs to ride, go home and put on clean clothes and shoes, get a pass and hop in back.
I just put on my asbestos underwear, go ahead and flame away....