HR, we're talking about an Enstron here. You can lose the engine, eat a candy bar, then drop the collective to start autorotation.
Ok, I'm exaggerating, but the Enstron requires nothing like the hair trigger response to lower the collective that a low inertia rotor system like the R-22 needs. You almost have to be asleep at the controls to lose that much rotor RPM. The only drawback to it's high inertia rotor system (which ATPMBA pointed out), is that if you do somehow allow the rotor RPM to decay too low, you can get in trouble getting the RPM back up again, especially at too low an altitude.