This product sounded too good to be true, but it's amazing! I have a computer in a room separate from our cable modem/router, and used to have a long ethernet cable stretched across the flat to use the internet. I plugged these in and without any set up at all, my computer was connected to the internet at high speed. I am completely impressed by them and would highly recommend them.
In case you're wondering, they work absolutely fine with macs.
The only reason I've downmarked them a star is their physical design. Each unit is quite tall, and if I plug them into my power points in the baseboard, they are so tight against the floor that I can't plug the ethernet cable in. So I have to plug each of them into a power bar, which is then plugged into the mains. Such a shame, as it would have been absurdly simple for the plugs to be rotated 180 degrees, making them fully usable in any plug. I suspect power points in continental Europe must generally be higher off the ground and that the design was created for that market.