Mira could pilot a tricked out Goliath, but everything is aftermarket and overheats with too much use. Also, prest 3 seems like it was meant for solo with Zeratul, since you wouldn’t get the 3rd fragment or any of its benefits for his units: shield guard without reflection shield, void templar without respawn, immortals without their health regen barrier, etc.
So this should change to: get as many fragments as you can in 20-25 mins but you don’t get the avatars. Today in Starcraft 2, we're going to be looking at some Brutal Co-Op Commanders. And yes, they last the “normal” shadow guard duration (annoyingly, prestige comes in after mastery.
However, combat units deal 50% less damage and Stasis Ward lasts 75% shorter.