The Bottom Line: The MyPetzl Light iOS app is a convenient, free, and slightly extravagant add-on to the new Petzl Nao and REACTIK+ headlamps. It doesn't really add anything other than some admittedly cool gimmicks to a headlamp. I was going to include this in my review of the REACTICK+, but the complexity of the app justifies its own review.
I've used Reactive Headlamps for a while now, and I am used to plugging them into my computer and adjusting the settings. It has been a really handy feature that has allowed me to customize the battery life of my headlamp. The downside is that I almost always forget to change it out of my base setting. So as much as Bluetooth feels like a very extravagant addition to a headlamp, I've been surprised that I use this feature more than I thought.
The biggest reason is that I like being able to get a brighter or dimmer profile for certain trips. Sometimes it's going to be a long alpine start with a major hike out afterward, so battery life is key. Sometimes it is night laps skiing, and max power is the name of the game. Being able to do that in the moment is pretty cool. And since it displays estimated battery life remaining, you also get a great up-to-date idea of how much of a charge is left.
I was initially concerned that it would drain my headlamp and phone. Thankfully there are multiple profiles to choose from. Basically these profiles are light settings that are set to work with specific sports. You can also add your own profiles, and the tool gives you up to date ideas about how much the distance and battery life you can expect. It is really quick and easy to swap profiles, so you waste minimal battery life. Just make sure to disconnect the headlamp or switch your phone back into airplane mode when you're finished.
One other really interesting feature is that you can adjust the beam from your phone. This I don't really use, but it's a nifty feature. Lastly, there is an SOS feature. You type in your message, and the light will relay the message in worse code. I doubt I will have battery life left in a time where I might need this feature, but it's again, it is a rather creative use of a headlamp app.