My bicycle commute is ~ 18 miles roundtrip and takes about half an hour each way. This year I decided to commute through the winter as well -- because it is frequently dark, I had to find a suitable commuting light.
I started off with a Planet Bike 1W Blaze, and this was great for a BE SEEN light and ok for a bailout light if I got caught commuting home at dusk in the summer. As it got darker earlier, I upgraded to a 2W Blaze but found it to be inadequate for lighting the paved trails in the early morning and early evening. (I currently use the 2W for my BE SEEN light.)
I considered the Light & Motion Stella 200 as well as the Dinotte 200L but really didn't want an external battery pack. Enter the Niterider MiNewt.250 Cordless. The profile of the light is similar to the Blaze but a bit longer. The mount is a little bulkier so the light sits up a little higher than the Blaze.
The light is supplied with an AC adapter, USB-mini USB cable, bar mount and helmet mount. The cable plugs in via USB to the AC adapter, and the mini-USB end plugs into the light. You can charge via AC, or via a USB port on your work computer. Nice! The power button is located on top of the light and is easy to press with gloves on. The power light is illuminated either green or red when the light is on: green when you've got a lot of juice, red when you have a little bit left. When the unit is charging, the light will turn green when the light is fully charged. Convenient and logical. Charge time according to NR is ~ 4.5 hours, which seems about right. I haven't run it all the way down yet, so my charge times are a little quicker but it certainly takes a few hours.
The beam is reasonable. At first I was expecting the trail to be lit up like daytime but that wasn't the case. Problem was that I was comparing it to an older Niterider HID Blowtorch light that I use for nighttime singletrack mountain biking. I'd estimate that I get a good 10-15 feet of illumination in front of the bike. Riding at 17-18 mph I don't feel like I'm outriding the beam. It is an order of magnitude better than the PB 2W Blaze, and a guy on the trail last week commented that the brightness of the light made him think that a car was coming up behind him. As far as offroad use goes, I think it would be a decent backup light. I wouldn't use one of these as my primary nighttime singletrack light, though. Incidentally, the light is bright enough that if I activate the strobe, I get a headache and feel like I'm going to have a seizure. As a result, I have the Blaze 2W mounted side-by-side on the handlebars with the MiNewt.250. With the Blaze in strobe, cars (hopefully) see me but the strobe doesn't distract me because the flashing street signs and license plates get washed out in the brightness of the MiNewt.
I haven't used the helmet mount, and at 190g for the light, I doubt that I will. When I compare the Blaze and MiNewt in my hands, though, they feel about the same.
The bar mount sucks -- the ratcheting mechanism is designed poorly or the teeth are cut wrong, or something. It holds the light ok but if the road is bumpy the mount will shift a little. I think this happens because the clamp is very difficult to ratchet down tightly. I couldn't crank it down nearly tight enough without rubber spacers on 31.8 bars, so I'm using the thick spacers. The spacers at least give the mount a little more grip to prevent it from rotating around the handlebar. For urban commuting this is probably ok -- nothing has been jettisoned over 500 miles but it makes me wonder about using it on a mountain bike.
In the final analysis, you get a self-contained, easy-to-use, bright-enough-for-nighttime-city-commuting light. It's super convenient, easy to put on / remove, and the USB charging option is great. I'd love more lumens but I suspect we're a bit limited by technology and battery size. A user-replaceable battery would ideal for longevity, and the mount is a minor travesty, but I can live with these issues. I think the overall package is a great value and it's ideal for my use.
UPDATE 2/27/2011 - To followup on the bar mount issue -- I've done some commuting in the rain and fog and find that once moisture gets between the mount and handlebar, the clamp will just flop down, pointing the light at the ground. Annoying. I've talked to the people at Niterider about this and their design team is looking into this. (They weren't really able to reproduce this problem, so I'm not sure how aggressively they are going to try to correct the issue.) In the interim, they've suggested putting down some waterproof cloth tape on the bar where the clamp gets mounted. Searching the internet I find this problem mentioned in several other forums, so I'm reasonably sure it's not just me being inept. Incidentally, the Planet Bike 2W Blaze mount that I run alongside the Niterider doesn't budge at all in the same conditions.