I found the sweet spot!
Barry Gibson, Head Professional of St. Vital Golf Centre in Winnipeg, Canada writes:
"I got my order today, super fast... very cool. It will be great for teaching! Not to mention this is the first time in years I've actually hit the sweet spot of my putter! Always found it to be a little strange to be more comfortable hitting a 3 iron over water than a two foot putt! Thanks!"