Hi Muck
You are correct in that you can log 50% of the time.
The system works by using the planes at night when they are not been used for training. They have a roster and pair up pilots to share the cost.
The school wont let you fly solo, normally one pilot fly’s the leg and the other guy acts as safety pilot (radio etc) vice versa on the return journey.
This time is permitted to be logged as PIC for both pilots as far as FAA are concerned.
JAA does not recognise 'safety pilot' so these logged hrs mean nothing if you are going for JAA licence issue.
In a nutshell you can only log (for JAA) the hrs you are handling pilot.
Even still £80 per hr as handling pilot (P.1,Twin) in the logbook is cheap in comparison.
Just be careful on your conversion back in the UK I got stung an extra £2500 because I chose the wrong FTO and subsequently moved elsewhere!
Good luck & have fun
Aircart
P.S. Suggest you visit Bombardiers on a Wednesday night!