Okay, my Flash-Cap finally arrived today, first impressions; It's actually pretty bright. The business end is essentially six LEDs in a ring, three that point straight out and three within the clear reddish casing that point somewhat outwards at an angle. It's plenty for navigating around indoors with dark-adjusted eyes, and perhaps to some extent even outdoors, as the three straight-out LEDs actually do throw a bit of a beam, comparable in throw to a decent keychain light.
The whole package adds an inch to the length of the Mag, and is its own completely separate circuit powered by four button cells with a very solid/quality feeling center switch. The cabbage-red transparent casing makes for quite the showpiece, displaying the LEDs and IC board/chips within. All of which is mounted atop a remarkably heavy-gauge flat black anodized aluminum cap (it's a single piece of machined aluminum; the endcap that the LED assembly sits on is roughly 5mm thick!)
The light has two modes, click for constant on, click off, click for blink, click off, repeat. Blink mode turns the light on/off roughly three times a second, with the on and off intervals being equal in duration (like a fast turn signal, not an instant flash/strobe). There's a slight delay between the click and the light coming on, so the aforementioned IC chips are clearly not just for show.
Also included is a powerfully magnetic base (also very heavy black aluminum) which screws into the base of the light assembly when it's not on your Mag - theoretically you could store/carry the magnet cap and the stock Maglite tailcap, this would allow the Flash-Cap to instantly become an adhesive work light or strobe while you continue to use your Mag (stick the Flash-Cap on the underside of your car hood to light the engine bay while using the Mag for spot lighting, for instance). There's also a lanyard rope and clip included, if you want to carry it like a flashlight or wear it around your neck.
Overall it's a solid piece of engineering, with a lot of forethought having gone into the design and a lot of quality in the individual components. Aside from the "how many different ways can I use this" factor, this also bumps up the safety use and value of a Mag considerably; in standard use just walking down a sidewalk for example, you now have a complete traffic-compliant lighting system - a headlight up front and a taillight in back. Plus you can always just use the Flash-Cap when the full power of your Mag isn't necessary, saving your primary batteries for when you need them.
Glo-Toob's Flash-Cap is definitely worth the $30 if you think you have a use for it. I can post some pictures if anyone's really interested.
