What about the A109 as an option for doing your IR?
I'd asked a similar question (AS355 vs A109 for initial twin TR and IR) of a seasoned UK pilot - he said there wasn't really a lot to choose between them, although the A109 TR would probably be a bit more useful in the long run.
The thought process behind my original question was that I felt there was more chance of getting some co-pilot work on the A109 than the AS355. I don't have any figures to back this hunch up, but just a general feeling of the UK charter market.
Simon
PS I haven't yet pursued the TR or IR, so I can't give a definitive answer!