It's a long way off for me (probably 18 months or so), but this is the route I will most likely take.
I don't view it as "short-cutting the whole JAA system", because you still need to take a flight test with a JAA examiner, to exactly the same standards as if you'd done the full JAA IR course. In fact, you will probably end up with more hours of instrument instruction, from a wider range of instructors, and in a wider range of environments, than if you did the standard course.
As for being asked why you chose this route, simply answer with the truth. I don't know what that is for. It might be money, or convenience, or simply because you'd never flown in <insert your favourite ICAO country here> so thought you'd go there to get an IR. For me, it will be because I will have trouble getting the time off work to do the (very long) JAR course, and I don't want to relegate such an important part of my training to weekends. Far more convenient to do an IMC rating first (which I don't mind doing at weekends). The IMC hours will reduce the time I need to get an FAA IR, so getting the boss to give me time off for that won't be a problem. And then, 6 months later, I will take another break from work to do the (minimum of) 15 hours conversion and the JAR test. I will be practicing my instrument flying on a regular basis as soon as the CAA send me my updated license with my IMC rating on it, so my total instrument time will be far higher than someone who has followed the standard route - but the main advantage is that it fits in with my current lifestyle. I can't see why that would be a problem for any potential employers.
As for the cons, there is only one I can think of. Every JAR state must recognise a JAR IR if you did the full JAR course. However, if you convert from a non-JAR IR, states other than that which issued the conversion are not obliged to recognise the conversion. So it might be that (for example) the French CAA will refuse to recognise your IR, which would rule out getting a job with a French airline. I haven't heard any real-life stories of anyone who has had a converted IR either recognised or not recognised, but since my French isn't good enough to work for a French airline anyway I'm not too bothered.
FFF
-------------