Before you go ahead with the purchase of the Synergy unit, I think it'd be a good idea for you to obtain the actual calibration chart that John claims he has for the unit without the variable control. He should be able to send you a table of numbers which is similar to what is on the Plasmafire website here for their Beta II unit:
http://www.plasmafire.com
(the site seems to be down at the moment but it should be back up shortly)
When I asked John about a calibration chart about a month ago, he seemed to have little clue, and that led to my decision to forego the Synergy unit and went with a Plasmafire unit. I'd be interested to know if John has brought his unit to be calibrated since then and produce a calibration chart.