I have bought this light on November 2016 and I do take my time when it comes to post a review so I can use the item and see how good/bad it is.

All I can say about this light is that it literally exceeded my expectations, it is indeed super bright. I thought I had a bright light before but now I can see I was wrong.
So far I have not yet encountered any problem with it, it works perfectly. I do not ride when it's raining so I can't say how effective the water proofing is.
I have an AERO bike and it fits the handlebar however, it is a little bit tight to get it in but once it does, the light is secure.
I will soon add pictures of it and if possible a small video of it.

I spent way more time than I should have comparing bike lights, but hey, that's bike geek thing. I thought I'd share and maybe help out someone else.

For me it came down to the Cygolight 550 and the Light and Motion 350. Both had good and bad reviews but there were more comments about short battery life on the 350 so (for me) that tipped the scales to Cygolight. I've done about 4 night rides and I couldn't be happier with my purchase.

Pros for the Light and Motion (based on reviews) is practically waterproof and has "˜sidelights'. The Cygolight is "˜water resistant' and no sidelights. If you want to take the light on and off the bike all the time you might prefer a rubber strap mount but I leave it on and prefer the solid screw mount of the Cygolight. I'm starting to use the light more even during the day-so it stays on the bike.

This Cygolight has 6 settings high, medium, low, medium/flashing walk and strobe. Unless you have terrible night vision you probably don't need more than medium most of the time- medium also extends the battery life. (It does remember the last setting used). High is very bright and low is great for dawn/dusk riding. (I don't depend just on the light. For night riding I also bought a reflective road worker vest. I see some people riding in all black and they wonder why drivers don't see them.)

The strobe is plain obnoxious. Strobe is not usable at night because after a few seconds you start getting dizzy. If you use it during the day angry drivers will likely try to run you off the road :) It's still brand new but so far battery life is great.

The charging port is accessible while it's on the bike and it'll run with the battery plugged in. A helmet mount would be nice but for <$50 it's a great buy. I assume I can get a helmet mount for a few bucks if I choose to. Summary is it's solidly built, looks good and it's bright.

Just got this light. I did quite a bit of research before buying this light and it seems to work great so far. It is PLENTY bright enough for my MTB so I wouldn't go any higher than 500-600 lumens. Although I haven't compared this to any of the cheaper products "claiming" the same or greater lumen rating, I think this is like most electronics in that you get what you pay for. There's no way that you can get a decent light claiming 900+ lumens for $29.99 without it either being a flat out lie or a P.O.S. or both. I highly recommend this light. The mount is easy, well designed, and works great. I was worried that when riding on bumps it would shift around but it seems to be very securely mounted. The release feature is easy and this light will work great as a simple flashlight also. Stay away from the cheap lights, stick with the reputable brands (Cygolite, Light & Motion, Cycle Torch, etc.)

The Cygolite Metro 550 USB light is bright, rugged light for my urban commute, but a few drawbacks are holding this light back. The power button requires a moderate amount of force to press, which is not just inconvenient, it can be a little dangerous. When I'm riding on well lit roads, I keep the light on blink mode for maximum "be seen" visibility. When transitioning into unlit streets, I want full and steady brightness to see the road ahead. Toggling the light takes a hand off the handlebars for at least a second longer than it should, which is especially unwelcome when riding over uneven, bumpy streets. The light's mount works effectively and is suitably stable, but the quick release feature takes more effort than it should. The light has also been resistant to water so far, including rides in moderately heavy rain. The light and mount have held up well to wear and tear too.

Assuming the limitations I mentioned aren't relevant to your ride, this light offers a nice amount of brightness in a sturdy package.

I like it, very bright and mounts just fine. Comes with two layers of spacer things, one of which I had to remove to get a proper fit on my larger-than-normal 8mm circumference bars.

Gets a star knocked off because I've had it come flying off the mount after a hard bump (I think it was a rare occurrence because I often hit hard bumps and this thing stays put). If you downhill mountain bike, I don't think this light will reliably stay on by itself without modification.

Also when the battery is not fully charged, this thing will do three short blinks exactly every 25 seconds when in high brightness mode (38 seconds or something when in medium brightness). I don't know if it's a feature telling you to plug it in or what, but if it is, it's kinda silly because the battery lasts for at least another 40 minutes after the blinking starts. Either that or the one I got is a tad messed up.

Also, it uses USB mini, not the regular usb micro that your phone and everything else uses. Annoying to have an extra cable lying around. Not too hard to replace the plug-in if you have a soldering iron.