The other main advantage is that with a US registered aircraft is that once the initial CofA is issued then all the owner has to do is make sure he keeps up currents Airworthiness Directives issued by the FAA. If this is done then the CofA is current and there is no requirement to outlay a few thousand punds every couple of years to those nice paper pushes.
For me the main advantage would be the right to exercise FAA licence privledges which are a damn site cheaper to obtain. I have used American Flight Services in Norwich and they are very good. Last time I went up they were hiring out a PA28 at £55/hr!!!!!!!! If you want to buy your own aircraft they can even let you know when one comes up, Tom Houston who owns the school is an American, either in the UK or through contacts in the good-ole-U-S-of-A!
Trust companies charges range from £300-1500/year.