The Olight puts out more lumens 250 vs 200, longer runtime on high, 3hrs vs 2 hrs.
It's 3 hours on an 18650, where it's not regulated, and you aren't getting the full 250 lumens. This is not a big deal imo, just trying to set things straight. Mine is a bit finicky sometimes about changing modes on 18650's, although generally it all works fine.
The low of the Olight is 7 lumens for 150 hours vs the LX2 low is 15 lumens for 47 hours. Also the Olight has a medium mode of 90 lumens for 12 hours.
The low and medium modes on the Olight are very nice. Unfortunately, you have to switch through a strobe mode to get from high->low. This is a very unfortunate feature, in my opinion. (It is the only thing about my M20 I don't really like.) The low and medium modes really are very useful and very well thought out, in my opinion.
I havent seen any reports of the clicky mechanism failing in an Olight M20. Looks like a really well built light.
I had a great deal of trouble with mine. I had to tighten it several times. I seem to have gotten it right now, but it took quite a bit of fiddling with it to get it right. I contacted the manufacturer about it at one point, which brings me to the one point that isn't stated in this thread - warranty.
The warranty on the surefire is significantly better than on the Olight, in my opinion. If your Olight breaks, you'll need to send it back to the maker, with a nominal fee. (I think $5 is what they told me - I may be mis-remembering that - it is no big deal though.) Even for something obvious, like a faulty switch. This is by no means a bad policy - however, the one warranty issue I've had with a SF (the switch on my M3 was faulty), they simply answered the phone, said "wow, we're sorry about that", and sent me a new switch. No fee, no questions asked.
Having used both warranties, I found the SF approach to be more to my liking. Again, not trying to overly criticize Olight - the Olight M20 is a GREAT value, and I don't regret owning it. But you should take service into account when comparing them. Having used both warranties, SF is better. (It should be - you paid for that too!)
I think the build on the Olight is quite good, although it is not as good as SF, in my opinion. (Although not as good is still extremely good.) Part of the problem, I think, is that the light is more flexible, and therefore slightly more failure prone. (Simple tends to be more bullet-proof.) Whether that is a big deal or a complete non-issue depends on your use and your personal preferences. The extra flexibility of the M20 is NICE.
I'm probably going to buy an LX2 btw - I have several other SF lights, but not that one. (Sorry I can't compare the LX2 directly to the M20.)
I think the good news here is that you don't really have a bad choice - both lights are excellent.
