These switch plates are milled out of 1.6mm black FR4, which is PCB material. The plates are lighter than their metal counter parts and have a little bit more flex.
The Hybrid Hotswap plates are meant for the Boardwalk Professional 2 Hotswap PCB but are compatible with the regular soldered Boardwalk as well. However, the Hybrid Hotswap plates only allow for a full ortho layout with either 2x 2U space bars in the bottom row or 1 7U spacebar.
The "soldered" plates give you the most layout options and are therefor meant to be paired with the soldered Boardwalk PCB.
Note: the images show the switchplates as green, they are however black.