This is the problem with cheap generic LED lights from China, they rate them at 1200 lumens or some such extremely overrated number, which by the way Magic Shine does as well, and the light is actually closer to 120 lumens, the Magic Shine isn't quite that bad they're about 50% off. However, for $35 or so their not bad. And this doesn't even take into consideration reliability issues found in these cheap lights.
I also agree with SIXTY FIVER, for road use I think some people are going way overboard on lights; you're not going to come in for a landing on a runway at night, so to have 2500 lumens is just plain nuts. I think the sweet spot in road lighting is right around 750 lumens max. I have a Philips Saferide that on comparisons it appears as bright as most 1000 lumen lights, I rarely put it on high, I run it mostly on the medium setting which is about half as bright as high and I'm an older man of 60 with dimmer vision than most young people, and at half brightness I have no problems seeing far enough ahead riding at 21 mph or faster to make a sudden stop or to avoid something. By the way, the same is true with my Cygolite MityCross 480, I rarely run it on high either, usually the medium setting. That's why I think right around 700 to 800 lumens is the sweet spot for max output and about 450 for most riding purposes. OF COURSE THIS IS JUST MY OPINION.
After using it for some time, I have come to really like it. I think in the beginning I didn't charge it enough so it wasn't bright enough, plus my stupidity in not plugging the connector all the way in. Now after 5 40-min rides on 'high', I still don't need to recharge it. I like it better than the 800lm flashlight I had used as it's lighter and smaller, easy to mount. Only minor inconvenience: full charging takes too long, connector too hard to remove (very tight, have to use pliers).
I've got the original Magicshine MJ-808 and the clones -- both recent and older. The MJ-808 was rated at 900 lumens, and was believed to be 600 lumens or so real-world. The clones that came out shortly after put out about the same amount of light. The more recent clones (the one that's $16 on Amazon now, to be precise) have more modern emitters and they claim 1200 lumens, and put out a good deal more than the MJ-808. I haven't measured it, but I've heard 900 lumens or so is about right, and that seems about right, compared to the MJ-808 and assuming it's 600 lumens.
The only real difference is in the battery pack. Geomangear sent me a pretty high quality pack replacement for the one they said was bad (though it was fine for me), and the clones still use what seems to be just like the original pack.
And like you, I usually run my lights in medium or low settings rather than high as well -- but it's nice to have the full 900 or so lumens available if I need it -- in a dark area, it's nice to have.