“Amazing, as long as they’re pointing up when they fire.”
No, the modern ones (depending on model) can be used when inverted assuming the pilot has adequate altitude. I think the biggest constraint is the speed of the aircraft. They’ll still go but the wind will cause serious injury.
They accelerate out at 10g and some can be used from ground level.
AKA which work at zero airspeed and zero altitude. Theoretically, at least, and in practice they're almost that good.
But you don't want to be in one that goes off while you're inside a maintenance hanger.