This is not a big deal....For 135 training and checkrides I teach it to all my pilots and have them demonstrate it to me. The FAA requires 1500 feet, but in reality you can recover from the initial indications with less than 100 foot altitude loss. Working fires, the times I get into it is coming in hot to a dip site...so I, and the guys I work with need to understand the symptoms and INITIAL indications.....we would probably not recover from full blown VRS at 100ft.
Here is how I demonstrate it---may not be perfect, but it works for me:
I have the pilot fly the aircraft in straight and level flight and then execute a slight nose up attitude and reduce power to less than hover power and HOLD it. Do not do anything else---the aircraft will decelerate, (it may take a while), and as it comes below ETL it will start to descend....again just HOLD the attitude....this allows you to differentiate between the loss of ETL and incipient VRS. Once you feel the nose shudder, you can execute the recovery with less than 100 foot drop from that point.
There is NO need to scare the student/pilot....the purpose is for them to recognize the indications etc.....