Brian Hoey's thing is that he comes at the Royal Family from the perspectives of their servants. This, as one might imagine, gives a very particular viewpoint. For example, whilst there are plenty of little anecdotes that show how fussy and demanding the Royals can be (Prince Charles, for example, insisting that his meals end with cheese and biscuits with the biscuits warmed to exactly his preferred temperature), the examples are told with an air of awe rather than ridicule. It also means that the text concentrates on matters such as clothing, food, cleaning and payscales rather than on matters of state. Of course, that's not a criticism, merely an observation.
The writing itself is plain and journalistic (that's a euphemism for not very good). There is no real narrative sense and details are mentioned in one chapter that are then introduced as though they were new material in subsequent chapters. It does get repetitive, especially with regard to the pay and progression This is also the material which will date quickly and render the text obsolete.
As a lifelong public servant, find it interesting to see how other departments operate. The Royal Household, despite its quirks and focus on delivery of domestic tasks, sounds very much a government department; the palaces sound very much like office blocks sharing space with relatively modestly sized Royal apartments; and the Royal roles sound quite straitjacketed and governed by protocol and expectations. These are not necessarily new insights but the way in which they are illustrated was interesting enough if, by the end, somewhat repetitive.
This is a light, frothy read. I guess it didn't take long to write and it doesn't take long to read. It is amusing in places and passes the time, but it is unlikely to offer any new insight into the monarchy as an institution, although it does shine a light on one or two of the personalities on both sides of the green baize door.