Is not a major difference (or one of the many paperwork drills required by the CAA/JARS/EASA) under the FAA system one does not have to have a Maintenance Manager overseeing the maintenance and only requires sign offs from engineers holding an A&P license with the IA authority?
CofA airtests become far less burdensome under the FAA system as well.
Pilot wise, for private /not for hire flying, it is much simpler as well. One must do a Flight Check (1179 ride ) every two years,which can be done with any FAA CFI licensed for the class and catagory of aircraft (CFI-H). Also remember no such thing as QHI, CFI and all that chin music) in the FAA System.
Your medical renews your license ....currency is done by flying ...stay current IFR and no annual checkride is required.
The Biennial Flight Check should be appropriate for ratings ,certificates (think License) , experience and Types (over 12,500 pounds). That ride can be in any helicopter but usually is preferred to be done in the most complex but not required. A proper Biennial flight check should exceed the eqivalent 1179 ride and in most cases amounts to something just shy of the initial Private or Commercial check ride with an extensive bit of ground work and quizzing about the aircraft, FAR's, Weather, flight planning, Weight and Balance, navigation, instrument procedures and the like.
Technically the Biennial ride is not a "check" ride but is more along the lines of certifying competence to exercise the privileges of your licenses. The ride should be as much instructional as to mere checking knowledge and ability.
Your insurance provider will also set requirements that might exceed the basic FAA minimums in order for you to be insured.
Given the choice of going N registry and FAA PPL in the UK or going the CAA route.....answer for me is simple. Usually if one can afford a helicopter in the UK, a trip to the States every other year is not a big expense knowing the Biennial Flight Check can be done in one day unless there are some hiccups.