The little, apparently plastic, J-shaped device is simple to use—the hook end is inserted into the chamber area of an unloaded firearm, and lights up the bore so one can make a visual check for fouling, obstructions, or evaluating a cleaning job.
Birchwood Casey also recommends the UV bore light for use as a chamber flag.
Nothing wrong with getting multiple uses out of a single tool, though we caution to then use that bore light to check for obstructions after using any device as a chamber flag that could potentially leave “shavings” in the bore.
These little gadgets are just $5.40, come two to a package. Too bad the holidays are past because these would have made excellent stocking stuffers.