I am one of the people who went over to the states on a j-1 visa and are now working as a flight instructor.
For insurance some schools require their instructors to have 300 hours and some only 200.
The school I work for requires any pilots they train to have only 200 to be a CFI but if they are hiring from outside there own School they require 300.
While I have do not have a JAA certificate, I am more than happy with the standard of my training, and the people I have spoke to say there is not much real word difference between the FAA Vs JAA if you go to a good school.
Give me a shout if you have any questions.