This is my quick and dirty review of the new Streamlight Protac Rail HL-X and comparison with the Surefire Scout M600. The SL rail series of lights work with Scout mounts, which is awesome. I have mine mounted on an Arisaka inline keymod mount. It is nice and close on the 45. One thing that I did not like is the tail end of the body protrudes further than the actual Scout. I was not able to use both the screws for the Arisaka, so it's held on by the lugs and one screw. It's secure, but I'd prefer to use both, and if I had a very short torx 90 degree key, I probably could use both. The body of the HL-X is a little bigger than the M600, as is the head. Not to the point of being obnoxiously big, it's just noticeable. The M600 just feels very sleek in comparison. It's bigger because it runs on "dual fuel", which allows it to take both CR-123's as well as 18650 rechargables. I have the handheld version also which I use for duty, and I do use 18650s, but I use regular 123's in the rifle light. The HL-X came with rail grippers for the tape switch, zip ties, and screws. It has a clicky tail cap as well. The tape switch has grooves for zip tie attachment, and holes for screw attachment. The screw holes line up with keymod spacing, so you could potentially use longer keymod screws and nuts and screw it into your keymod. I opted for the double sided sticky tape for now. I like that the tape switch has a constant on clicky at the back. The M600 tape switch does not. Another thing I really liked about the tape switch is the tail cap allows it to fold in rather than stick straight out the back. Gives you a little more room behind the light to work with. On to the beam...It's advertised as 1000 lumens, 27,100 candela. This isn't super scientific, however I did set my cell phone camera to pro mode with no auto settings, and used the same settings for each photo, so it shouldn't be adjusting for light. At 10 yards, I think I prefer the M600. The hot spot is large and defined, and the spill reaches a wider area. The HL-X has a slightly smaller, but still well sized hot spot, and decent spill. At 25 yards, the HL-X has a nice, large hot spot with very usable spill. The M600 has a nice hot spot, but the spill starts to fade out pretty quickly. At 50 yards, the HL-X still has a nice hot spot and the spill illuminates a decent area around it. The M600 has a workable hot spot, but the spill does nothing. At 75 yards, the HL-X still has a very workable hot spot. You'd still be able to identify targets. The spill is still illuminating the building. At this distance the M600 is still illuminating the building with the hot spot, but your ability to identify targets is decreased. At 100 yards, the HL-X is illuminating the building with enough brightness to see targets. Identification without magnification would be more difficult, but there's still plenty of light down range. The M600 is barely illuminating the building at this point. At 150 yards, the HL-X is still illuminating the building, but not with enough intensity to identify targets very well. The M600 is no longer useful at this distance. Obviously the Streamlight costs a hell of a lot less than the Surefire. I think I got this one for $80 on pre order, which was a steal. I haven't run SL tape switches, so I can't attest to the durability of that part, but I can say that I've been running TLR-1's for a long time and they are good to go. Streamlight customer service is top notch too.