If you're considering the TriNewt at all, then look at the DiNotte 600L too. The 600L battery is much more compact (fits under long stems nicely) and the whole 600L system is about half the weight of the TriNewt. Plus you get two batteries with the 600L, if that matters
The DiNotte also does not rely on an O-ring type of attachment.
You may find this review worth the reading, if you're considering off-the-shelf systems:
http://gearreview.com/LEDs08_intro.php and the TriNewt and 600L are under the "Large Array" category.
The TriNewt is a plastic housing with three LED's, right?
Aluminum. LOTS of aluminum (read: way more than necessary). Great if you need to drive nails during a ride, or club an attacker.