This is a very old posting, but in case you're reading, the current version of the Blackburn Mars taillight has a snap closure and no longer uses screws to hold the battery cover in place. It is quite bright from both the rear and sides and very well made, in spite of its low cost. The use of AAA batteries keeps the unit lightweight, yet I still get good battery life, in spite of using rechargeables. It comes with a variety of mounting options, including a neat rack mount that attaches to the reflector bracket of a rear rack. It also has a built-in belt clip, when all else fails. I've used these for years, along with several other styles, including the ridiculously overpriced CatEye LD1000. Although I wouldn't touch the rest of the Mars lighting series, the taillght is my favorite of all the blinkies.