CustomDUO LED modules are not compatible with new Petzl Duo Z (and Duo S) models, released early 2018. These new Duo models are a fully sealed design and are not upgradeable, and while they can be helmet mounted, we understand that this is limited to the Petzl Vertex and Alveo, not exactly the cavers preference.
The new Duos are aimed principally at the high volume industrial workplace market, probably with half an eye on commercial outdoor activity providers. There is a 4xAA version and also li-ion battery pack based models. With slick marketing, these will no doubt sell in good numbers to their principle target audience. However, from a cavers perspective, it would be very difficult to make any positive argument for the new z2 Duo, versus the original pre 2018 4xAA Duo. But the gear shops can only push what is currently available, and the new Duo is already being discounted !!
The original Duo can of course be upgraded with LED modules that feature the very latest, most efficient LEDs. CustomDUO modules currently provide approaching 200 lumens per watt, far beyond the performance level of mass market lights using unspecified LEDs. The LEDs used in the new Duo z2 are not specified. However, tech info states that it has 4 mixed flood and spot LED light settings from 50 lumens (15 hours) to 220 lumens (2 hours), plus a 430 lumen short burst feature. This performance information is sketchy at best, but suggests (as you might expect) that light efficiency, output and run times are well below what is readily achieved with a CustomDUO LED upgrade, original Duo and some good quality nimh AAs.
The superior performance and upgradeability of the original Duo aside, the advantages continue. From a cavers perspective, the original Duo is robust, light weight, easy to operate and significantly cheaper than the new models. It is simple to swap batteries, and is easily and securely helmet mounted. It is immediately compatible with most helmets, including models typically preferred by cavers. Importantly, from a caving perspective, the original Duo is also depth rated to -5m, and can withstand a little bit more than that.
We could go on, but you probably get the idea. Things just don't always get better. Did we mention the 6000-7000K Light temperature? ugh ......
From a caving perspective, it's got to be the original, upgradeable pre 2018 Petzl Duo when compared with the new version.