Bear in mind if you do the FI in the uk taking advantage of the 50 hour total time reduction you rating will not be valid in other JAA states as it is only the uk that has this difference.
Whether your rating will become valid when you get to to 300 (or 300 + 30 hrs fi course) i don't know.
South Africa has some demand for Jaa instructors, employment restrictions for foreigners very restrictive, but the operator don't seem to care.
As with most things in life - don't get caught!