I would suggest that transmitted interference is an essential risk with this kind of device, since the mains wiring which is unscreened forms a great big transmitting antenna. How much of an effect you see depends on geometry, frequencies in use, length of transmitting and receiving wires, susceptibility of kit to received rfi vs how well it filters the incoming noise out, plus all the other factors that I have forgotten just now.
It's not worth the risk, and if you have neighbours, then I would have to say that it is arguably irresponsible, but that's me being harsh. I certainly wouldn't be at all happy if I found one of these devices in use next door to me.
If you've had no problems with them then fair enough, no wish to cause offence to existing users. This is just my own opinion. :-)