This is a great combo light/laser. Good quality, enough light power to be used with a handgun, and easy/ergonomic operation.
It comes with several adapters to fit a variety of handgun rail spacing to help position it as desired by the trigger guard.
The laser sighting went smoothly and it seems firm; I haven't tried it at the range but comparing with other similar lights I have, I feel confident that it will stand the stress.

Great light/laser combo if you don't want a weaponlight that sticks out too far.

I personally want the light shorter I'd not flush with the crown of the barrel. Steamlight is a reputable brand so I'll nitpick. The key system is unnecessarily complicated and requires you to carry other keys for different firearm manufacturers--not exactly universal, unlike my Surefire, which you just attach and detach to any picatinny rail.

I use weaponlights on a USP9 full size (with Surefire adapter), and an FN5.7, which requires two different keys for the TLR-4, to prevent the light from sliding forward and backward depending on the rail. Surefire doesn't have that problem.

Also, the laser is at the bottom of the housing as opposed to being closer to the bore axis. I understand the thinking behind the design, especially if the TLR-4 is mounted under a longer barrel, but then again, buy a light that matches the gun. With a USP, a blocky gun to begin with, plus the adapter because of H&K's proprietary system, plus the housing for the light, puts the laser over an inch below the barrel. Universal holster carry would be tough.

That inch difference means a lot if you swap the TLR-4 to another handgun. The laser will have a different point of impact, and before anyone says the shooting distance will be close enough that it doesn't matter, I say every bullet fired is a lawsuit waiting to happen. Definitely zero the laser to each pistol before carrying.

I purchased a warehouse deals unit that came missing the e-clip that holds the rail on. I'm not deducting the star for that, as there's a good chance it just fell out and I missed it (it's a 1/8" e-clip btw, Home Depot sells it in a 2-pack but Lowe's does not!). I'm taking a star off because the mounting system just seems really kludgy and prone to error. The directions could be a lot clearer and don't really explain why you're mounting it the way you are.

That having been said, it's important to note that you NOT tighten the light as tight as you can get it on the rail; this is how you break the plastic half of the rail mount (which really should be metal - the real reason I took a star off!). You just tighten it until it doesn't wiggle any more.

As for functionality, I haven't actually shot it since I installed it (range time is expensive) so I can't give a good review on longevity, but the light and laser both work very well. The laser adjustment is fairly easy as long as you take care to fully insert the included allen wrench before twisting it. The switch is easy to use and is well placed.

All in all, for the price, it's a great deal, and as long as you are super careful with the instructions (other reviews here give great instructions) you'll have a good unit.

I got this for my KSG. I installed it on the HiTech Side Rail so that it does not interfere with the sight picture over the top rail, and also does not jerk back and forth during cycling. I am right-handed and put it on the left side. After cycling, my left thumb is in perfect position to activate both the rotating power switch and the light/laser selection toggle

Contrary to some reviewers, I have no problem seeing the red laser dot, even at relatively long distances, say 200 feet or so. For an extra $100 you can get the green laser, which appears brighter to the human eye..

My only complaint is that the print in the operator's manual is very small (admission: I am over 40 years old). I had to look at an online manual ([...]) and magnify it a few times. I would recommend to Streamlight that they include in the manual a small section where they identify each part that is referenced later. For example, I had no idea what the "e-clip" was until I matched what I saw in the (magnified) pdf with a tiny little part in the bag of rail keys. I didn't take off any stars for this because I am probably the only one in the world with this problem. :)

Overall rating: A+

This worked good, mounted on my AR15's quad rail, put at left side just within thumb reach to
activate LED light and or laser.

I used the "E" key to mount to the picatinny rail (it comes with many keys for various rail widths / types).

Since it's really for the bottom rail of a pistol, it does stick out a bit on my rifle, compared to using
a light without laser add on.

For the coin, with both a bright light and laser, it's a decent setup for a rifle. Wish it had strobe function.

Probably could be used on the lower part of rail (underneath rifle), and possible still activate it but I'd have to remove my sling since it would obstruct the light and laser.

It's a perfect setup on the left side of the rail as I can effortlessly activate either momentary or constant LED light, laser or have both on, using my left thumb.

I've not fired the rifle with it yet, not sure if it can hold up to recoil, but for AR15, there's not much of that.

I'd think if it's design is for a pistol, it should hold up for an AR15 rifle as a tiny pistol has lots of recoil compared to
the AR15 rifle (at least my 45's, 40 cal and 10mm's do).