I used to "chop" throttle all the time on my students. But i had my limits, never under 50kts, never under 1500ft AGL, and never during a climb (high MAP). I never had any problems. You just have to be prepared to dump the lever bloody quickly if the students doesn't react, and also haul the cyclic back to get the RPM back in the green. And you also have to fully prepare the student by 'building up' to the engine failure (announce, lower, and roll off SLOWLY the first few times)