On the mind of many people, the best lights for is with high Lumens. So they would like to search some high brightness lights, such as the light with output above 2000Lumen (like MJ-880) or higher (like 2200lm Spiker 1207)...but is it really a right guide? What do you think about this question, on the basis of your professional experience-is it true that high lumen lights are best for MTB?

If you are going to ride off-road, yes, you want to throw a lot of light. You need to see the terrain to read it and decide which line is best, especially when coming down hill. A handlebar mounted light is good but you really want something that you can shine where you need the light which means a helmet mounted light. Handlebar lights shine where the bars are pointed but that light is pointed to where you are now. You need to see where you are going next and handlebar mounted lights are often not pointed in that direction, especially on corners.

As for which light, that's a matter of opinion. First, neither of the lights you have listed have the output they claim. They can't, the emitter doesn't have that kind of output. The maximum output you can get from a Cree XML-T6 is 692 lumens according to Cree's specification sheet. The max you could get for an XML-U2 is 742 lumens. With two emitters, the maximum output is 1384 and 1484 lumens, respectively. And that's under laboratory conditions. The output will be less in the field. For comparison sake, it doesn't matter because nearly everyone at this price and low inflates their output values. Just keep that in mind when shopping. There are lots and lots of lights out there that are far cheaper with the same output. Even the optics aren't all that different. For example, these guys sell a very similar light to the MJ-880 for $48. And if you don't like the bat wing thing, these guys sell one for $40. I purchased this light from Fasttech and it's a good light of good quality. It's a bit floody for my tastes...I prefer a tight spot light for off-road...but it is small and lightweight. My daughter is using for her commutes and says it's a good light. I don't think I'd use a dual beam for a helmet light but that might change. The Yinding is smaller than my current single light. If it were a spot light, I'd use it in a heart beat.

I would suggest not putting a lot of money into any LED light right now. The market is changing rapidly and the prices are falling to stupid levels (you can find lights for less than $20). Spending a lot on the light now makes little sense. Investing $50 in a light that you might be replacing next year with an improved model hurts less than spending $200 on the same light.

https://flashlightwiki.com/Cree#XM-L
https://budgetlightforum.com/node/19331