I have no doubt that clinical UV wands can pretty effectively sterilyze surfaces, if bright enough, long enough, and short enough wavelength. Really effective ones will give your corneas a sunburn....
But they are not low powered, long wave UV lights generated by LED bulbs powered by batteries. Nor are they inexpensive, small, or light weight.
I suggested sunning ones mail on each side in bright sunlight for an hour or two, if one has concerns about the possibility of a viral load on their mail. CDC has assured us this is a low probability.
Regular sun borne UV light is remarkably effective - if one cultures the surfaces of sun exposed roads or parking lots the amount of bacteria or fungi alive on their surfaces is actually rather small.
I was involved with some remediation in a health care facility years ago and I would see the colony counts of the agar test plates in rooms, hall ways, office surfaces during remediation - frequently in the ~30,000 - 60,000 on an exposed open plate. A control plate from the parking lot outside the building in sunlight would be 30 colonies, or 50 colonies. But from a wooded garden over 250,000....
One must know how to intepret test results, or they can easily be misconstrued.
We all live in a biological stew daily.
Re my doubts about many UV wands effectiveness - The Federal Trade Commission seems to have doubts as well.
Further investigation reveals UV-C LEDs that are used for water and air disinfection - typically germacidal UV light is about about 270 or 280 nanometers in wavelength. Most of the LED UV-C emitters I can find are all about 395 nanometers in wavelength - like I said, longer and less energetic from a microbiologic standpoint.
It turns out I already own one of those UV-C flashlight sterilizers with 51 396 nanometer wavelength LEDs - I bought mine 5 years ago when it was recommended to make pet urine flouresce in carpet - no mention of sterilization then, and having used it, it does make pet urine flouresce, but it is a very weak source of UV light. Maybe - MAYBE - if one exposed a small surface item at a distance of 1 cm for 40 or 50 seconds it would sterilize the surface of a key or something. A toilet seat would easily take half an hour at that rate - Lysol or bleach is faster and much cheaper in terms of sweat equity.