Excellent light, very bright. Has a variety of brightess and blink pattern settings. Easy to use. Mounting and attaching/removing is simple if you just need a seat post mount. Good customer support from DiNotte.

Mounting options are limited if you don't want to use the seat post. The AA batteries pop out of the holder unless you tape them in, which is a pain if you need to remove the batteries to charge them. You have to be careful how you mount everything so the light doesn't come disconnected from the batteries. When the light is getting inadequate power from the batteries, possibly because it's raining or the batteries are low, it enters a reduced brightness non-blinking state where it can't be turned off, which can lead to surprises.

I purchased this taillight for commuting after dark and for use in the rain. DiNotte was the only manufacturer of taillights bright enough for commuting use. It's as bright as a car taillight, maybe even brighter. The brightness is amazing. It has plenty of brightness levels and blink patterns, and it's easy to control these settings.

The light doesn't come with a wide array of mounting hardware, just a plastic piece and some elastic rings that allow you to attach it to your seat post. But it works well. It can be removed or reattached in a few seconds, in case you don't like leaving your light on the bike where it might get stolen. I never used the light on my helmet so I don't know what that's like.

The AA batteries are convenient because you can keep charged batteries on hand (I use Sanyo Eneloop rechargeables, which don't lose charge on the shelf) and swap them in instead of waiting for a recharge. But the AA system also causes problems. The light uses a generic external battery holder that holds 4 AA's. The light cable snaps onto this using two contacts like you'd see on a 9V battery. The holder fits into a little pouch that you strap onto your bike with a velcro strap. I strap it around the seat post, where it stays pretty well on my bike, and I wrap the light cable around the post. If you have a bag blocking the rear view though, the hardware isn't adequate for mounting it elsewhere (like on a rack). The biggest problem is that the batteries can very easily get jarred loose from the battery holder. I have to tape the batteries into the holder with masking tape. That makes it a pain to remove the batteries to recharge them. Also the cable came disconnected from the battery holder for me once, so I have to tape it or be careful how I mount it. It's a generic battery holder that you can buy anywhere, which I think was DiNotte's goal, but without a better holder the idea is flawed because off-the-shelf parts aren't designed for the bumps, vibrations and weather conditions of riding.

The other quirk is that when the light isn't getting enough power, it goes into an always-on, low brightness state according to DiNotte. In that state, you can't turn the light off except by unplugging it. This happened to me once on a rainy day, presumably because water interfered with conductivity to the AA's. The batteries and connectors are exposed to the elements. The light went back into normal operation about 10 minutes after I got out of the rain. I didn't use the light in the rain after that. It also happened in my garage once when the rechargeable batteries got too low in power. The light came on when I wasn't around and stayed on until I discovered it hours later, because the light goes into always-on mode. So you should always disconnect the light from the batteries when not in use (I don't know if this happens with the lithium-ion setup). While DiNotte couldn't cure my problems, they explained why this was happening and were very responsive and answered my emailed questions right away.

The light itself is great. The AA setup is problematic. If you want a more dependable setup, you can go with the lithium ion version. That's much more expensive of course. I plan to get the new 300R which integrates the light and LI battery come as a single unit – with no cords or battery pack!

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Planet Bike Superflash light, many cheap taillights.