OK, here is my story and data:-
After deciding I needed dew heating, I read all the reviews I could.
Last year, I purchased the Thousand Oaks controller and Dewnot heater straps and the Astrosystems DG1 secondary mirror heater - all from SDM Telescopes and for a lot less than the current list prices (had a win on the exchange rate!)
I got one heater strap from a US supplier - threw it into an order to get the best shipping deal.
I know you don't want the DG1, but for information, it is an intelligent heater with a sensor on the mirror and one in the ambient air. It maintains the mirror a set amount warmer than the ambient. Just feed it with 12V. The Thousand Oaks controller has a straight through (uncontrolled) 12 V out. Some people power their Argo Navis from here. I power the DG1.
I measured the resistances of the Dewnot heaters tonight and the current they drew from the battery, through the controller. I have a 10A panel meter in the battery line so I cannot read any better than 0.1A. I wasn't going to wire a multimeter into the line tonight, sorry.
To finish the DG1 story, it drew a steady 0.2A current, whether heating or not (according to the indicating LED)
Now, the resistances of the Dewnot heater straps:-
DNO11 (10" - to heat my eyepiece box) 9.7 Ohms
DNO09 (8" - to heat my C8 corrector plate) 13.2 Ohms
DNO04 (3" - to heat my finderscope objective or a DSLR camera lens) 24.5 Ohms
DNO03 (2" - to heat a 2" eyepiece) 38.0 Ohms
DNO02 (1.25" - to heat a 1.25" eyepiece) 48.7 Ohms
I connected the controller to the battery. The current draw of controller was not detectable on the 10A panel meter.
The controller works by delivering a proportion of the duty cycle from 0% at "OFF" to 100% at "HI". At the "MED" point, it seems to be delivering 50-60% of the cycle. That is, it cycles the output on and off, turning the heater current on fully for more and more of the cycle as the knob setting is increased. At HI, the output stays on 10% of the time.
At the HI setting, the battery drain was:-
DNO11 1.3A
DNO09 1.1A
DNO04 0.5A
DNO03 0.3A
DNO02 0.2, maybe more like 0.25A
Hey, Ohms law generally works - not sure about the 8" strap!
I turned the DNO11, DNO09, DNO04 and DNO03 all to HI and the meter read 2.9A. Seems a bit lower than the sum above, but we are in the right ballpark.
I fit the DNO11, DNO04, DNO03 and DNO02 to my 12" dob. At that stage, the controller is fully utilised. Now, even on the dripping nights, I've never needed to be higher than MED on the controller, so I'd guess I'd be drawing an average of 50% of 2.4A = 1.2A (plus the steady 0.2A to the DG1 makes it 1.4A). I've never pulled much charge out of a moderate size gel battery over 4-5 hours. (plug the 12V, 90W hairdryer into the parallel socket and that's a different story. But it has stayed packed away since I installed this dewheating.)
I second John's comment of the desirability that the Thousand Oaks controller can have the low voltage cutout disabled. This is designed to prevent you drawing so much power from your car battery that you have insufficient left to start the engine.
Yes, the dewbuster is more elegant since it senses temperature and delivers only the heating required. The Thousand Oaks, however, does what works for me.
That was a useful exercise for me. I need to check where I can connect a little AC mains powerpack (DC out, but even AC would work) and power a dew heater in a situation where I cannot use the controller. (Some folks at Snake Valley will recall this cable hanging through the air connecting the controller on the Dob to the corrector plate heater on the C8. I ran into it a few times!
To comment on Rob's experience. I would normally cap the eyepiece in the focusser if I'm stepping away. I routinely have the eyepiece in the focusser fitted with a heating strap. It's nice to put your hand in your pocket while having coffee in the kitchen, feel the eyepiece cap which should be on the eyepiece, and think - doesn't matter. Sure enough, mist and dew all around but that glass is crystal clear when you walk back to it 15 minutes later!
I hope this information helps.