My floor pump came with the old head, which was always iffy from the get go, but just suddenly stopped sealing one day after frankly not that much use. This one ... at least it's not a guessing game of did I get it on right, but the first tube I tried it on, it doesn't work with. For some reason. All my other tube stems work great, but the one on my rear trainer tire, it's like it doesn't screw down quite far enough or something and the stem valve never opens. Oh well. At least it works most of the time.
I run a Garmin Varia radar taillight, which is great except its daytime flash is 65 lumens, not that bright. So I got this for its as a second, brighter taillight: 300 lumens daytime flash with a 5 hr lifetime (or 150 lumens for 7hr). This unit works beautifully, and, given its 11 (!) modes, it's really helpful that it "remembers" the mode it was last in when you turn it on again, so you don't have to click through all those modes.
One improvement would be for Lezyne to bevel the light's rubber mount so that the light would sit nearly vertical on a seatpost instead of shining slightly downwards. Most seat posts lean towards the rear, the mount should be redesigned to compensate for a "typical" seatpost lean.
I ride only in the daytime, bought this for its 1000 lumen daytime flash mode and 7.5hr lifetime in that mode. Very bright and its flash sequence is definitely attention-grabbing. Given that it has 8 modes, it's great that it "remembers" the mode you last used last. When you head out for your next ride, you simply hold down the power button until the light turns on, about 2 sec. When you finish, just hold down the button again until the light turns off - easy.
A few niggles:
(1) gotta pull hard to fix its rubber strap around the handlebar, helps to rotate the light 45-90 degrees on its mount
(2) to avoid reflections off the screen of my Garmin (on its "out front" mount), had to mount the light upside down below the handlebar, putting the power button underneath the light where I can't see its state of charge indication - move the power button to the rear of the unit (or have dual power buttons, top and bottom?)
The light appears to work as advertised. I use the daytime mode and it is very bright. Haven't measured the battery life, but it appears to be about as advertised.
Charging the light took some adaptation. It's not easy to unhook it from the handlebars each time to charge it, so I wound up putting a USB charger on an extension cord and charging it on the bike.
I lost the rubber boot that fits over the USB connector within the first month of use. Lezyne claims there isn't a design problem and you just have to make sure it's pushed on firmly. They're sending a replacement under warranty, I'll make sure it's pushed on firmly, and hopefully it'll last.