There hasn’t been much discussion of batteries, probably because that knowledge is assumed by many, but I think it’s worth talking about.
The Fenix HL21, 2.625 oz. total with strap and one AA battery served me well for years with Engergizer Ultimate lithium batteries. But got tired of constantly throwing the batteries out, as they are expensive and toxic. Now use a ThruNite TH20, which takes one AA sized Lithium Ion 14500 battery, which is rechargeable, and lasts me much longer on one battery. The lamp is a little heavier, at 3.5 oz total, but is quite comfortable at that weight, although I would not want anything heavier.
The 18650 rechargeable Li-Ion cell batteries have more capacity, but are larger and heavier, and I’ve not been able to find a headlamp using an 18650 that is as light.
I see that the Petzl lamp you mention can be powered by a Petzl Li-Ion AccuCore cell equivalent in size to 3 AAA cells; a good development, as I found using Energizer Lithium AAA cells that were not rechargeable to be even more expensive and wasteful, and that was the reason for moving to the HL21.
I would go with a lamp that can be powered by one of the rechargeable Li-Ion cells (carrying one charged extra as back-up), and among those, choose the model that best fits your needs. The rechargeable Li-Ion batteries have much more capacity than older types, and in many cases, such as the TH20, will throw a much brighter light when you want it. The only other consideration would be weight, of course, and some of the Petzl lamps that also work with AAAs can get up over four oz. with a Li-Ion battery, which as in my case, might be more weight than you want.
REI has a number of these products, both lamps and Li-Ion batteries, on its site and might be a helpful place to look at first. Note that the Candlepower and similar forums do not take weight into consideration as much as we would like. I also found that even when specifying the weight of stripped down lamps (without battery, headband or bracket) weights were understated by manufacturers and sellers by as much as 30%.
And a final consideration, as has been much in the news lately, many of the Li-Ion batteries being manufactured present an inherent danger of fire or explosion. That might be a reason for leaning toward a more established manufacturer and retailer; but as we’ve seen, that alone may not be a foolproof approach. It is the reason why I’m willing to carry a headlamp with a slightly heavier aluminum housing, store high drain batteries in strong airtight containers, and recharge them in a safe and protected place.