Which is really the best method? What gets the ducts cleanest?

Also, some companies now offer the installation (for about 0) of in-line UV light (which kills mold, bacteria). Does anyone have one of these units? Does it help you?

Note: Change the 3M disposable furnace filter every 3 months, & ductwork is 10 years old & has been cleaned twice before, but not by truck-mount method.
aswkingfish: It seems like a lot of expense and time to find & buy a portable air-monitoring device and go through all you describe. One method must be better than the other & I hope to choose from anecdotal input from people who have perhaps tried both.
Travis – an electronic ionizing air cleaner..the kind that uses ozone to clean…ground-level ozone is horrible for asthmatics (my daughter, as you surmised), but UV light is what hospitals use to decrease bacteria/dust mites.
And I don’t believe it’s a hoax, because when I had it done after the 1st 4 years in this house, there was a lot of dust that came out of my ducts. I watched them work.