When we replaced the HVAC system in our lake home 5 years ago we did include a UV light in the air way.
It is as advertised....it does keep the airway from the blower forward into the home as clean as the day it was installed.
Because the home is only utilized at different times of the year, mostly summer months...there use to be a light coating of a powdery type of mold on the leather furniture and wood surfaces.
Since the installation we have not had one spec of the powdery deposit.
The bulb (about 20 inches in length) requires replacement annually as the UV strength degrades some with time. The bulb costs about $69....less from Amazon....which I now replace myself...takes about 5 minutes.
When it comes time to replace the HVAC here in FL the new system will include a similar HVAC system including UV light.
This link is a similar system:
HVAC UV Lights for AC Systems-Do They Work? - House So Green
We have experienced non of the issues that were commented on in the references.
Do your home work. The technology does work.