It's so unbelievably shit for anything else than tele GC ... basically only usable in one situation that never happens : when you're stalling and you need some building/unit to finish asap. When you're not stalling, i believe it's just faster to use the BP of the engi.
But even in this situation how do you know how many engi you need to finish up something ? Like for example, how many t1 engis to finish 10k HP of an unfinished GC ? Many times i've tried to use this to finish a unit, and ended up not having enough engis ... So you're left with no engi, and your stuff still unfinished. Game over.
Now i pretty much never use it or even think of it ... it's just so risky to use wthout clear indicator of if you can finish the building or if you'll just suicide the engi for nothing