They're certainly cheap. The only real reservation I have is that the spec says nothing about encryption. If you're going to transmit your own confidential data via the mains wiring, you would be well advised to make sure that it can't be picked up by your neighbours.
@Stuart: The software is very possibly required for enabling encryption (assuming that these devices support it). Some devices like this need to be connected to a Windows machine all the time they're being used, because the encryption software runs on the Windows machine and isn't saved in the powerline device. The only brand which I've found to be fully Linux compatible is Devolo - they provide Linux software, and it only has to be run while setting up the encryption.
