Bicycle headlights serve two functions: they help you see where you are going and they help other people see you. That second function, what I call the "be seen" function, is very important but often the manufacturers, consumers and marketeers of bike lights focus all their attention into placing the brightest possible beam the farthest distance down the road or trail. If you are looking for a light that will let you confidently descend a mountain pass at 30 miles per hour at midnight or navigate your favorite section of twisty, rooty singletrack at two AM on a moonless night, the Cat Eye EL-210 is really not the light for you.
The EL-210 is a very nice "be seen" light. The EL-210, like all the lights in Cat Eye's EL line of products, use light-emitting diodes (LEDs) instead of traditional light bulbs. The LEDs in the EL-210 should never burn out and cast a white beam with a slight bluish tint, somewhat reminiscent of bright moonlight. Rather than placing a tight beam far down the road, the EL-210 channels the light from it's five LEDs into a broad puddle of light. Those five LEDs are driven by four AA batteries and Cat Eye claims that a set of alkaline batteries will drive the light for 200 hours in flashing mode and 100 hours in constant mode. The flashing mode is a pretty high frequency flash (at least several times per second) and it's very attention grabbing.
Unlike some of Cat Eye's other lights, the EL-210 ships with a set of batteries in the box so you could buy the light, strap it to your bike and ride right home. The light mount is a quick-release clamp that installs quickly without tools. I've had some past problems with the heavier Cat Eye lights vibrating loose from their clamps, so I advise wrapping a rubber band around the light and clamp just to make things a bit more secure.
I prefer to use rechargeable Nickel-Metal Hydride (NiMH) batteries instead of alkalines in my lights and the NiMH batteries work fine in the EL-210. Even if Cat Eye's battery life estimates are optimistic, I should be able to run the EL-210 for several weeks worth of dark commutes between battery charges.
I've commuted the past couple of nights with an EL-210 on my handlebars. The wide beam is quite nice for much of my familar urban commute and it actually works better than I expected on the dark sections along the Sammamish River Trail. However, I think most riders would want to use the EL-210 in conjunction with a more powerful light for fast riding.
The EL-210 does not have the impressive weather-proof seals found on some Cat Eye lights like the EL-500 and the EL-400 but so far I have not had any problems with water getting into the light.I would caution riders not to mount this light upside-down however as that would probably cause water to seep in and collect in the light. The better sealed lights don't have this limitation.
At about $30, the EL-210 does what it's supposed to do. It's compact, very eye-catching and has great battery life. It's a pretty good light for casual use and it would be a good companion light when paired with another more powerful head or helmet light.