Obviously everyone has an opinion, and some have had a bad experience I am sure it happens now and then, and probably with any shop, my wife dove with the shop that does the cruise lines and had a terrible dive, but we do not hold that against them.
having Dived With Martin for more than 200 dives I can say I have never had a dive limited by anything other than air or bottom time. they have nitrox or large tanks or anything else you might like if you ask ahead of time. I have dived every known dive site and then some that are not listed. Every dive master I have met there is very proffessional and experienced, there turn over is not noticable in my 6 years of being their customer. And they will pick me up at any hotel I stay at, I believe they have more boats than any other OP, only because any time I dive with them I see several of their boats as we pass by.
they take small groups but can accomodate large groups if you like, they are flexable and willing to accomodate any reasonable request. they take care of my gear in between dives, and I take care of their DMs because they earn it. If DWM were the most expensive I would still dive with them, if they are the cheapest then consider it a bonus. I am not affiliated with them in any way, but I do love the shop and the people that run it so I will continue to save money with them.