A convenience, NOT A SAFETY! , "All-OFF" is
trivial to implement with X10.
X10 is not at all common in the UK (remember we have 240V, 50Hz mains, so
just shipping X10 modules from the states doesn't help), and it's expensive.
And if you think I trust electronics in place of contactors, you can't
know me very well :-) (quite apart from the fact that contactors are
easier to repair!).
-tony