This product has a lot of negatives to it: the bulky design is heavy, the bizarre strapping system won't work on all types of helmets (bike helmets are totally out - or really any helmet that doesn't have a flat you put the torch straps under) , the thing is an ugly duck - lots of demerits.
The shining (ha!) star of the NAO is its reactive lighting, which is great, works as advertised, can be customize-able, but the downloadable app is cheesy and customize-able settings are not very amazing. The battery life is honest-to-goodness incredible - most especially because of the reactive lighting saving juice when you don't need it: i.e.: looking at something close up, like what's right in front of you. I don't care about any of those other things I mentioned, because of this killer feature.
Except, let's talk about this included proprietary battery.
Don't lose it.
It's actually easy to lose, since you need to REMOVE it from the head torch itself to recharge. That's horrible design. If you lose it, there's no way in Hell an outdoor shop will have a replacement in stock, and there's a good chance in a few years that Petzl won't have one available, either. Try finding a replacement for NAO that's 2 generations old. I'll wait.
Let's talk about the battery itself. Open it up, and you'll find what's basically a stock 18650 rechargeable lithium battery! EXCEPT, there's all these specific electronic parts soldered on, so you can't just pop in a new 18650 battery and be good, you need all the custom electronics. Petzl made that design intentionally - you can't swap in a 18650 and be good, you gotta buy a new battery pack from them, if you want say, a backup, or a replacement. Why not, I dunno, keep the custom electronics on the head torch itself and not soldered on the battery?
Like I noted, replacements are hard to find, even online, and Petzl doesn't make it easy to get a replacement for older version's of the NAO - Every version of the NAO comes with a slightly different battery pack - they're not interchangeable.
So you're SOL if you ever lose that battery pack. Which is a shame, since the actual battery itself is just wrapped in proprietary b.s., so even if you do purchase a replacement, it's a many times the price of a 18650 markup.
Petzl could have done this: have the battery be a stock 18650 you can replace, and also have an easy to way to recharge it through the head torch itself, via a USB plug which doesn't need to be accessed by removing the battery pack itself and using a female to female USB plug (a f 2 f is itself hard to find a replacement for, and yet another different USB chord I need to carry around)
In all, the NAO's design screams, "PROTOTYPE", but it made it to production anyways. Great features (REACTIVE LIGHTING), but the package/design is horrifyingly bulky. The new iteration didn't change any of that - you can't polish a turd.
"Nao" that I have this headtorch without a battery pack (since I lost it!), it's a paperweight, unless I want to cough up $70 for a replacement battery. That's right: $70! 40% of the entire price of the light. For a $3 18650 lithium battery, and probably $1 worth of custom electronics.
Bad show, Petzl!