TV network execs would have setups like this, though usually 3 color displays and a switch to select the sound. So they could see when the competition played commercials and such. But these setups were usually custom built by their technician depts. The only consumer applications I can think of would be hard core sports fans, say if a baseball game and a football game were on at the same time. rather small market.
The above set would predate picture-in-picture sets.
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