before I say anything else, I am known as a dealer for EZM (you are a customer of mine, and I thank you for that
I am in no way trying to pimp my product, just answering to the best of my knowledge
there a few differences that I see...
1 - the 'silent drive' is a manual, where the 'whisper drive' is an automatic
2 - the silent is designed for the higher-revving (7200 rpm)49cc Honda or HuaSheng, the whisper is geared for the lower-revving (5000 rpm)70cc Harbor Freight (both ARE adaptable though AFAIK)
3 - the silent is available now, and has been for 1 year, the whisper is taking deposits for when they are available to buy
I did wait to answer your question, because I didn't want to look like I was 'selling', but after seeing no other response, thought you deserved an answer from someone
BTW, did you know that EZM has an auto as well ?
, THAT was my sales pitch