Bruce there are a number of products on the market that are light cured resins, that might also be worth considering and a bit more suitable for some types of epoxy flies than Knot Sense, depending on what you're tying. Check out the webpages for these products to se examples of flies, types of products (different viscosities, "flex" versions etc) and their FAQ pages to get some more info.
Tuffleye HOME "TUFFLEYE"
There are a lot of excellent tutorials from some exceptional tyers on the site including Peter Gray, Jonny King and Bob Popovics. I think it's fair to say that this is the most popular and widely available of the specialty light cured products other than Loon. Tuffleye actually uses "Blue Light" a different wavelength than other products that use UV wavelengths so the flashlights aren't interchangeable. The Blue Light wavelength is supposedly safer (same as used by dentists to cure resins used in some fillings), but the flashlights tend to be more expensive, so higher start up cost
Clear Cure Goo Home
In addition to the "regular" hard cure resin, CCG is also coming out with a "flexible" cure version of resin, which is said to be like a silicone type feel--
and Bug Bond Home - Bug-Bond
Originally from Great Britain, it's now available in the US also. Both CCG and BB are UV cured resins and can supposedly share the same UV wavelength flashlight.
Although all these products work similarly in that they are resins cured with UV light, the wavelength of UV might differ-- so that UV flashlights may or may not be interchangeable. For example the same UV light can supposedly be used on CCG and Bug Bond, but not on Loon Knot Sense, and Tuffleye uses another wavelength altogether.
Once you get past the initial start up price (the flashlights can be expensive) these products offer some great advantages over epoxy --
With traditional epoxy products like Devcon 5 Min or 30 Minute etc that harden after mixing equal amounts of Part A and Part B goop, you generally need to either tie up a bunch of flies and mix up a batch of epoxy and do them all at once and worry about the last flies being covered with epoxy that's already starting to cure, or to mix up batches for 1 fly at a time and end up wasting a lot of unused epoxy that cures between flies. You also need to ensure you get a pretty equal amount of A and B goop and mix them well other wise the epoxy won't cure properly and will remain cloudy or tacky to the touch.
But perhaps the biggest issue with epoxy is that you generally want some kind of drying wheel that will rotate your flies while the epoxy cures-- otherwise the epoxy tends to sag and your flies will cure with a big wad of epoxy on the bottom of the fly. Traditional epoxy also tends to yellow with exposure to UV rays. The modern UV cured stuff is said not to yellow and remains clear.
Because the cure time is "semi-instantaneous" (if that's a word, meaning just a few seconds) once you hit it with the UV light, you don't have to worry about it setting too soon, and can work with it until your happy, then zap it with a light. Because you're doing the curing in-hand, with he light, you don't have to worry about the resin sagging while unattended during a long cure time, so you won't need a drying wheel.
Some of these products can remain just a little tacky to the touch after curing with the UV light and in some cases the manufacturers recommend a top coat of Sally Hansen's Hard As Nails over the resin after it's cured with the UV light, some are advertised as tack free.
I've used 5 Minute Epoxy for many years for saltwater flies like surf candies etc, and frankly didn't see what all the fuss was about until I started using some Bug Bond about a year ago-- It's soooo much easier to use than epoxy. But it also depends on what you're tying-- if it's to coat the backs of a few copper johns every year it may not be worth it, and it might be easier and more efficient to tie up a bunch, stick them in a block of styrofoam, and them coat them all with a dab of 5 min epoxy on the top of the wingcase and let them all dry. But if you want to tie stuff like shrimp, MOE style bonefish flies, surf candies and large epoxy style flies, or work with epoxy "in the round" like coating the bodies of chironomid larva/pupa patterns where traditional epoxy will have a tendency to sag while drying, then it's probably worth it if you plan on tying a lot of them.
Although the startup cost for these light cured resins sounds high, remember that you'll need to either make or buy some kind of a drying wheel for traditional epoxy flies if you don't already have one. You can easily make your own drying wheel for just a few bucks, and there are a zillion ideas on the web, but store bought ones can range from $30 to $80-- or about the same price as the start up (special light plus a tube or two) for one of the new light cured resin products that won't require a wheel for drying.
Hopefully other folks will weigh in with their experience with these products.