Wanted to apply the same treatment for ducts in my house... A friend was nearly killed by the contamination in his Miami house.
The pictured/linked product should be effective; but in my opinion, only to the area it illuminates. The rest of ducts length should be able to harbor plenty of undesirable microorganisms.
It may 'purify' some air flowing, but does it kill the existing germs anchored in the ducts ? Only setting the whole house on fire is surer.
Replacing the entire ducting with new one$ is I believe, unreliable, as the hands/tools/gloves of the working crew will spread the germs from the removed duct to the new.
and perhaps bring other types of germs from previous worked sites.
Found out a while ago, that ultraviolet LED should perform similarly well; can be run inside the whole length of ducts as a 'christmas' light string. May not involve voltage hazards, temperature, act nearly everywhere in the ducts, easy install, looong 'lamp' life, for 24/7.
Difference in germicidal wavelength from UV sources (LED, fluorescent, incandescent) attacks one type of microorganism better than another. But getting into analyzing which spore/mold in
your home is more susceptible than the other to decide the wavelength could be complex.
The difference in price to Honeywell may have something to do with their CEOs yatchs and golfing schedules that the chinese workers do not have.
Please continue updating actions and rationale about this subject.