If there is stuff in the ducts, the fact that it’s laying there and not being blown into the rooms is proof positive that it is hurting no-one. The 5-6 exceptions you cite in this article I’ll buy, but only with the caveat that at least some of those could have been avoided by proper protection (during remodeling for example) – and if asbestos/lead/whatever winds up in your ducts- the remodeling contractor should be the one paying to remove it.
Pay particular attention to cooling coils, which are designed to remove water from the air and can be a major source of moisture contamination of the system that can lead to mold growth. Make sure the condensate pan drains properly. The presence of substantial standing water and/or debris indicates a problem requiring immediate attention. Check any insulation near cooling coils for wet spots.
I called the company and John answered. We set a time for him to come over that was convenient for us both. He came exactly on time and went right to work. He removed all of the vent covers, including some screens that were over the vents that I had no idea were there. He washed all of the vent covers with soap and water and then started to vacuum all of the ducts, doing a complete and thorough job. He was extremely friendly, professional and worked quickly and thoroughly. He even checked the dryer vent exhaust on the roof to make sure it was clear. After he finished vacuuming the ducts, he sanitized them and then reattached all of the vents.
Simon and co. did a great job cleaning out the ducts in our house. He showed us how they looked before (with about a 1/4 inch of dust at the bottom) and how they looked after (almost like new with not a bit of dust left). He helped us find some drafty spots in the vents and was happy to help us fix those at no extra cost. Very professional and good work.