Shown to us at Bespoked Manchester, this is a singlespeed conversion kit for people who don't necessarily always want to run their hub in a 12 speed configuration and want to go back down to single speed - or vice versa. “A lot of people run single speed in the off seasons to practice and train and they didn't really have a good way to do it. So we created this kit to convert that SRAM XD hub back down to a single speed kit." Assembly is pretty simple, without the need for loads of tools. A sleeve that slides…
Crikey! This is a long way from the £6 DMR 16t cog and a bunch of cassette spacers that we used to use. (And still do).
An aluminium cog that wears out in a few rides is indeed fairly niche. Still, I'm sure it'll find a home on some pointless 'artisan' bikes that never get ridden.
Reverse components have had something similar for a while but with sensible steel sprockets. Still not cheap though