Did my FAA IR in the LA basin in 2000. Hardest thing I've ever done in an aeroplane including learning how to teach ADF tracking/NDB approaches and CPL test in 90F under JAA.
It's real world- you have to do a 300nm xc with 5 approaches IFR (did mine at night in Santa Anna induced wave rotor) and the SoCal RT is REALLY HECTIC (no 'Exam' callsigns and Gawd helpyer if you fluff and falter). Also the 3 hour oral is no picnic, managed to fail my 1st and not even get as far as the plane.
Yet to convert to JAA IR due to JAA CPL exams not being valid for an IR, so can't compare. Undoubtedly made me a far better pilot and more competent than I otherwise would be when teaching as an FI in the UK.
PF