The description of the Item reads "make sure all the plugs are in the same circuit." Does this mean it must be on the same Breaker in the electrical box or just in the same household?
Technology has changed a bit. The older model has much more issues crossing circuits. The newer units also use the grounding wires so they tend to work better. The new standard is called AV2 almost all adapters that say they are 1000 or 1200 or faster use this newer technology.
Same breaker. They can work if on different breakers but they don't work as good.
If they are on Different breakers, how much will the signal strength go down on average?
Using WiFi now and the router is on a different floor and it keeps dropping signal while I game.
Technology has changed a bit. The older model has much more issues crossing circuits. The newer units also use the grounding wires so they tend to work better. The new standard is called AV2 almost all adapters that say they are 1000 or 1200 or faster use this newer technology.
Same breaker. They can work if on different breakers but they don't work as good.
If they are on Different breakers, how much will the signal strength go down on average?
Using WiFi now and the router is on a different floor and it keeps dropping signal while I game.
A different breaker should have minimal effect unless it is old and corroded. Keep in mind most homes have two phase power. Most commercial power is three phase. The adapters should be on the same phase. You can use a phase coupler to merge signals on different phases.