Exactly Stuart,
That is what I have tried to get across, Rcds do have there valid uses. but also lead to a false sense of security, mind you the same applies to an isolation transformer, the point being if happen to come into contact with both feeds of the supply side of things then you get a belt.
We have had many heated discussions in the past
which one is safer, they both have pros and cons, the basic problem appears from time to time when people try to mix up different protection schemes in the mistaken belief that it is safer, which it isn't
Edit: in actual fact you are better off with the device under test (DUT) and the tests equipment both fully floating ie, the use of one or more isolating transformers (or battery powered test equipment) , this of course still won't prevent a shock if you happen to come into contact across a supply, which of course makes sense as that is the supply's purpose to power the load.