I had one of these added to a new A/C/furnace install about 6 months ago -
https://www.dustfree.com/products/whole-home-purification/micropure
The installed recommended it, and he didn't seem like a scammer - was making good suggestions in other areas of what was getting done.
But how to tell if it's helpful - I'm not sure.
I would have liked to have gotten a little air quality testing device a year earlier, and then see if anything changed after the new setup with UV also was installed.
Not sure even then I would be able to tell, though - my doors are almost always open to backyard and garage, so there's probably always things coming in and going out.
I guess I could still do a test with one of those testing devices, though... Just unplug the UV light for 6+ months, try to keep the doors closed more (pooch is going to hate me for that, but I guess doggie doors would keep him happy), and see if air quality starts to go down.
Then plug it back in and see if it improves?
When I tried to find out more about them, it seemed like there were two types. One is line of sight and aimed at the coils/drain pan where moisture can build up. Line of sight type UV is supposed to help with that, and is the less expensive type.
This MicroPure gets installed in the duct just after that, and is supposed to zap biologicals, etc... in the air as it passes by.
Whether the air is going too fast for it to do that - that's beyond me.
It's got a 2 year life-span of the bulb. So I may get an air tester device in a few months and see what it says over the next year, then replace bulb after that and see if anything changes the following year. If not, then I probably won't replace a second time. I'd also guess air quality could be different based on seasons - allergens, humidity, etc... so watching for a year both times to compare might help.