It depends on your background on how easy the transition is. To get all the exemptions you have to be very experienced on heavy aircraft. For example, I have been in the RAF for 16 years, have over 5000 hours, 2500 of those on 4 engine heavy jets and I don't qualify for all the exemptions.
Before I went down the CAA ATPL route, I was qualified to command a 4 engine passenger jet flying from a somewhere like LHR, across the pond in MNPS/RVSM airspace into somewhere like JFK. Now I have the ATPL, what's the difference - the registration of the aircraft I'm allowed to fly has changed!
But I'm glad I did all the exams, and I'm sure the knowledge of how to do manual air plots across the Atlantic or how Decca works will come in useful one day - maybe not!
My point is why did I have to do them in the first place!