a LOON brand light that I use to cure UV glue
Any of the "UV" "torch pens/lights" are nothing more than high powered black lights. Remember... you and I cannot see in the UV spectrum! Therefore, the term "UV" automatically becomes a gimmick! You can also think of it this way... Humans can get severe sunburns from UV light 91.5M-miles away (the sun). What do you think a true UV light would do 2 to 6 inches away from your hand would do?
When dealing with optical enhancers I imagine soft/natural materials will absorb the effect and some will make the effect pop. It will truly depend on the material.. Again, hard surface materials benefit the best (paints or plastics) due penetration and light refraction. A good example would be the ol' 1970's black light poster. These posters where painted in the brightest fluorescent colors on a semi-hard surface surrounded by soft, felt-like black material. Once the black light was turned on the fluorescence popped and the soft black material absorbed the light.
I hate to call out manufacturers, but the use of the word "UV" is the gimmick yet the effect is not scientifically proven- especially for steelhead. (We know that some species of fish use UV to hunt.) A definite thumbs up from me on salmon from me, but under the right conditions in the salt. You see we cannot, at this time, replicate true UV on lures/flies/boats. We can only artificially simulate a "like" effect based upon what humans see- not fish.
As mentioned above if you have confidence in the fly half the battle is won. If you have no confidence in a fly, why tie it on?