I saw it in one of the 3L webinars but my 3L seems to have shipped without it.
You can fixate the device to a table with two screws. It has two outlets for the “horns” on the backside of the 3L build platform. So you can fixate the platform to a table and can remove the models more easily form the platfrom.
I cannot find it in the formlabs shop and the support hotline allegedly never heard of such a device. Was it just a prototype and never shipped?