To my knowledge: Incorrect. Both devices have a "secret handshake", meaning they can only communicate with each other.
In theory you can connect thousands of them in a single home. What they all do however is transmit certain data of a power line. There more of these transmissions, the busier (thus slower). Keep in mind these things are not very fast compared to normal network infrastructure components.
Best usage is one close to your first part of the network (for instance, downstairs, connected to the modem or switch) and one close to your second part of the network (for instance, upstairs, connected to a single switch). This way you distribute your network load a lot.
Personally i'm still a bit paranoia about these things, since you are using the power lines for something different than they were intended to. No matter how much certification and quality assurance these devices have, they still do "things" that the power lines were never designed for.