The EOTW (easy-on-the-wallet) switch plate fits MX switches, and is made out of FR4 (PCB material).
EOTW switch plates are not compatible with Lo-Pro or Hi-Pro cases because they don't have any holes.
The Planck PCB (rev 5 or later) attaches to the bottom plate via 6 screws (screws are included with the Planck PCB). The space between the USB port and the bottom of the rubber feet (also included) is less than standard cases, so you may want to use a slimmer USB cable, or thicker rubber feet.