The shop I used to dive with switched from YMCA to SDI. The only thing involved for me was listening to a speakerphone for half an hour, and writing a check. I felt ripped off. I'm not familiar with PADI Master Scuba Diver, but YMCA has a Master Diver certification. The difference between that and Dive Master is an issue of liability. Dive Master is a professional track of education and master diver is a personal level of training. Is it the same for PADI?
Consider whether you intend to teach or provide support for the shop. Consider the issue concerning professional liability insurance. I left the shop I worked with, but have maintained both YMCA and SDI DM certifications, and now teach with an independent instructor. I am sitting for my YMCA AI now, and when I get it, I will apply for a cross-over cert. by equivilency to SDI.
Whatever you decide, make sure you are happy with what you are doing, why you are doing it and who you are doing it with. The agency on your card in much less important than the information you provide to new divers and the levelto which you provide your service.
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