On the subject, it appears that the changes in the 4th edition are soley to do with frequency of testing. I think that the responsibility of frequency will lie with the principal duty holder. It also seems that class 2 appliances in low risk environments may not need testing at all. Annual testing may not be required on many appliances, just a visual inspection by anyone with any sense.
With this in mind, with times already tough, possibly getting tougher, what's the point in paying £50 for the new book? I take it none of the tests or paperwork have actually changed? I know the labels no longer need a next test date.