In my research the most important element seems to be a layer of carbon fiber on the cover to protect against RFI and vibration.
Some forums recommend using a non-magnetic stainless steel cover. Available for quad receptacles.
These were highly recommended for duplex outlets...
Furutech 104-D Carbon Fiber Hi-Performance Duplex Outlet Cover Plate
Oyaide Electric High-grade Outlet Wpc-z
Some forums recommend using a non-magnetic stainless steel cover. Available for quad receptacles.
These were highly recommended for duplex outlets...
Furutech 104-D Carbon Fiber Hi-Performance Duplex Outlet Cover Plate
Oyaide Electric High-grade Outlet Wpc-z