I have one with the earths in accordance with the sterling power
diagram. It was not very expensive - £175 for a 3.6kVA. When I was
installing the shore power its use was instantly demonstrated whilst
still on dry land in the builders shed. The building's neutral was
showing +12 compared to earth, once onboard after the ship side neutral
had been bonded to earth, the ship side neutral was of course at Ov.
The other major advantage of an IT is that you no longer have to worry
whether the shore supply itself is wired correctly - Live is Neutral
and vice versa.