Yes, I have one in my air handler and feel it was WELL worth it. The bulb is the LIGHTSTICK 14" UV bulb, which I replace about every 16 months. It kills all of the mold and mildew way past where the light actually shines, so I know that it's working and effective.
I also know that it's quite powerful because if I use 3M filters of the "fuzzy" kind, like MERV 7, it will destroy the filter media in about 2 months. I called 3M on this and they basically said Tough S, the bulb is too close to the filter. It is actually, being only about 10 inches above it. I don't have that issue with other filter brands though, and I don't have that with the 3M "hard media" expensive, 1200 filters.
It has given me great comfort knowing that it is on the job over this past year.
Being in FL, and near the Intracoastal, there is a lot of humidity and the associated mold growth, so it is definitely worth it in my opinion. I also use the MERV 13 filters in conjunction with the UV light.