Bore light...
Big Fats--I generally use my thumb nail, too, and in decent light, with a firearm into which my thumb fits, that's all that's necessary.
Rebs--Almost any light you can get into the chamber of the firearm in question, will do the job just fine. Since bore lights can be had for less than $5, why is this a consideration? Just buy the next one you see @ the next gun show you go to--I'm sure it'll work as well as any other. This isn't exactly a piece of "fine machinery."
I've had 3 bore lights--One is just a piece of "J" shaped plastic, that bends the ambient light around into the bore of the firearm. One is the same piece, but attached to a small flashlight, so it works regardless of the ambient light. One is a flexible-neck LED. None was very expensive, and all of 'em work just fine.