There were lots of cartridge-switching devices marketed for pre-disc consoles, but Cardco, Inc. takes the prize for the most technically-detailed marketing, with this full-page ad devoted primarily to a single product for the Commodore 64.
Unfortunately, the many technical features detailed in the ad copy are easy to overlook when the product is named the CARDBOARD/5.
It featured high quality glass/epoxy circuit board, gold plated contacts, convenient toggle switches, and a full plastic enclosure. And its blinking LEDs were probably great for lending that sought-after 1960's Star Trek quality to the computer desk. And no doubt it was useful, especially with those override switches and convenient reset button.
But CARDBOARD, even CARDBOARD/5, just sounds cheap.