Runtime, output, general expectations? How does it throw? How about battery life? A good match for the Olight M31? My friend has moved me to consider getting one.
Saw this one...
http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=190603167797#ht_485wt_1130
My friend's Olight is top-notch. Only thing I have that can outshine it is the 980L.
XML is better than SST50. The Sky Ray SLT-V2 or FandyFire SLT-V6 (these two are the same flashlight) are the budget power choice. A little more cash can get you the Crelant 7G5. These two flashlights have quite a following on here. I have one of the FF V6 (modded with a 4A driver) and SR V2 and am pleased with both. With the exception of my modded light the XML run times will exceed the SST50 because it is a more efficient led. Brighter with less power = better emitter.
Oh yes, I have noticed how popular those are. I just figured driven twice as hard with large reflector would be appealing, but those are too long. I may give them a try, still, or try this one from manfont...
Big reflector has me going.
If you want shorter, cheaper , bigger reflector , mass alu , also take 1x18650 or 1x26650, forget your #2 link.
DX $35.60
KD $40.97
https://budgetlightforum.com/t/-/5251
The downside to the mentioned single cell flashlights is less light. According to the links both are regulated to 2200ma vs 3000ma of the two cell flashlights listed in post #2.
In reply #2 Rusty Joe prefer 1x18650 not too long, big reflector (mabe Change driver to V2 8x7135)
If he prefer 2x18650, IMO pls go to...
+1 $5 Driver 8x7135 good choice
The one SST-50 drop in I did have had a decent tint and was pretty much equal to an XML when both are driven to there limit. The only problem is SST-50 needs 5 amps to put out the same amount of light as an XML at 3 amps.
But.... SST-50
more expensive than XM-L
Bigger die : flooder
Hi thermal resistance
Hi Vf : 3A @ around 3.5V while XM-L 3A @ around 3.3 , XM-L is better for 1x18650 
SST-50 is outdated. Get XML!
You, sir, are a gentleman and a scholar! I'm so buying it! And I even like the form-factor.