Yeah I worked on Phi Phi. It is a good way to train and get experience at the same time. Often you will finnish and then find a job on phi phi or go on to instructor. Phi Phi is a great Island to work on. The flip side is that it is quite expensive to live on phi phi, so you end up spending what you save on course prices, you won't earn in those 4 months, so make sure you have enough cash for that time. The diving pretty much the best in thailand, better than in the gulf. Check that there are no hidden costs like equipment rental etc