You need to confirm what country allows for this agreement. Example I doubt Norway will, the ATPL exams as far as I know are normally under CAA UK, so this means your JAA IR training/ skills test must be in the UK.
I am fairly sure that all your skills tests, CPL/ME has to be done in UK airspace.
Going to the USA, will not make big difference in the price, when you add in all the extras, but of course it is nicer in the sun in Florida.
Probably will mean few extra hours, as UK airspace/weather etc. is not exactly the same as US, needs a little getting used to.
UK CPL skills test has a few nasty surprises, as your Nav target might actually be a wind sock from an old unused airfield from second world war in the middle of a field.
Has taken many US trained pilots by surprise. Norway would be easier to fly in, as terrain is more easy to recognize. But I believe all these JAA training schools are approved under UK CAA, it might have been changes lately that I am not aware of.
But normally you must do your skills test in the same country as your ATPL's are under.