Damo
I can only offer my opinion based on my own limited experience, and as I am only half way through my ATPL exams I don't have any first hand experience of airline interviews yet. However I have spoken to many people and read many of the threads here on pprune and I can't say that I know of anyone who has obtained a job, or even the advantage at interview because they have had some JOT training. There may be some advantage to it but is it a big enough advantage to justify the cost ? I don't know.
I still believe as in my original post that the airlines look beyond that to the person and your experience. Maybe it would be better as MAB suggests, spending the extra money on either some further training or some real flying time.
Realistically your first job is likely to be with a turboprop operator, so JOT won't be of much use in that situation. Then if you apply for a jet job in the future, a couple of thousand hours turbo time will give you a much bigger advantage than a few hours in a sim. If the airlines are recruiting low hour guys for jet jobs when you qualify, will you have an advantage over one of your peers because you have JOT and they don't ? I really don't know.
Will you have the advantage over someone with a few hundred (or thousand) hours experience under their belt ? I doubt it.
As I said at the top, this is purely my view on it but you have to make your decision based on what is right for you.
Regards
NHF