Jonathan G.wrote a review of Lezyne Helmet Mount on October 24, 2018
Familiarity: I've put it through the wringer
Another example of excellent engineering and functionality from Lezyne. Writing this review, so other bike-dorks know how to use this product with Deca & other light units.
I got the Deca Drive 1500i, and this light, but didn't correctly read the completely obvious note on Lezyne's site, which states this product requires a secondary adapter (which replaces the rubber strap), when used with units, such as the Deca Drive. The extra required bit is a $3 item not currently sold on CC: the "Handlebar hard Mount Adapter", which you can find on Lezyne's site.
The adapter is here:
magshop.lezyne.com (USA store)
Home>LED Lights>Accessories>Handlebar Hard Mount Adapter
OR (if CC doesn't remove this URL):