So you will not be able to go into nav mode and then hit left shift to boost (afterburner) away.

Nav mode doesn’t have boost with L-shift. Only SCM mode has traditional boost with L-shift. What Yogi was describing is that when a QD is active and your ship is affected by it, you can switch to Nav mode and your shields will get stored in the buffer, but you won’t be able to fly faster than unboosted-SCM speed. To go faster you would have to switch back to SCM mode and use your boost.

By all means try out Master Modes in arena commander. We don’t have QDs there yet, but you can get a better sense for how stuff works by using it.

You actually have normal thruster boost available in NAV mode.