I've got three in service at the moment, one connected to the router, one providing wireless coverage and Ethernet to the desktop PC at the back of the house, one in the workshop. They're on my list to check for interference, now I've finally got live error stats I can try to eliminate local equipment. Only problem is that DSL Stats runs on the desktop over the powerline adapters, so I'll need to rig up something temporary. All that I know at the moment is that they don't change attenuation or noise margin, nor do they kick the DSL off.