You know what you are doing and have chosen to use a safe interface as a result of your knowledge. That is not the case for many PICAXE users. How many students know about UL approval or CE marking? Interestingly, the very article you quote has the line "it is not recommended for casual programmers" which would suggest that such units might not be the best for educational purposes. Don't get me wrong, I'm not trying to slate X10 (although I'm not a big fan) and I'm not trying to put competent engineers off from using it. I simply don't think it belongs in an educational device where it would encourage the inexperienced to 'play' with mains operated devices.