The POM plate is a variable layout cut out of 1.2mm white delrin. It will support most vintage and modern keycap sets.
Metal versions of this plate are made for the Polycarbonate Lin Montage specifically, where the crest designs under the blockers will show through the frosted case. It is cut into 1.2mm aluminum and given a brushed finish. This plate is only suitable for AT101 layout keycaps and PCBs that support that layout (note the 1.5u stepped caps).
The leaf spring design was designed to slightly soften the harsh bottom-out of switches in these hard metal plates. It does not add vibration or a great deal of movement, but it does temper the typing experience.