I bought mine directly from the company, in fact I ordered it right from their web site. Showed up via UPS 4 days later. I called their office a couple times with questions, and they are great people to work with. It was in fact the Commercial Diesel model, with the 6mm transducer size. Cost was about $65 plus shipping.
I know it's not a "necessary" thing to have, you can run by ear alone, but it sure is nice to know where you are in the power curve. /forums/images/graemlins/cool.gif