Does this actually work at all?

I bought this after seriously considering the twice-as-expensive Kendrick alternative. One of the primary reasons for choosing the AstroZap product is that it includes a velcro strap to secure the heater, while the Kendrick product includes a rubber band, which I know will deteriorate and snap with time. I'm happy with the velcro, but the heater doesn't seem to succeed in its intended purpose of preventing dew. I've only had two suitable viewing nights since purchasing it (I live in Orlando, FL, where it can still be very damp in winter evenings) and my Quikfinder dewed up both nights, while my SCT's corrector plate, eyepieces and Stellarvue 50 mm Finder Scope did not. While it could be a problem with the way I've got the heater positioned (no instructions included, so who knows what the recommended position is?), I suspect the concept is flawed.