That's what I thought, until I suggested to somebody else that he use them to control some lights - who then turned around a month or so later and complained that the relay had given up the ghost... Could have been a bad relay, could have been the idiot wielding the soldering iron, who knows? Not all relays are intended to be left on for long periods, and I concluded that this was probably the case here. At 20 quid a pop I'd certainly prefer to err on the side of caution if it was my money.