My personnal experience has been like Ishi described. I had Japanese instructors in the SIM and have being flying with Japanese line instructors and I have to say that they have been very professional. Are they demanding and pretty inflexible about procedures and company callouts and the likes? The answer to that is without a doubt, YES! but from there to grabby?
Don't know about that? remember that the stories you hear from these training events are always the tip of the iceberg. What is under the waterline, you never hear about