We used Scubadu when we stayed at the El Cozumeleno last month. We hired the private boat (5 or 6 in your party to do that). Antonio was great to work with, he's very knowledgeable about the reef systems and the keeps the dive op from the El Coz running smoothly. He will listen to your needs/experience level/etc. and help you plan your dives. Our DM let us suggest dives and offered his advice also.
We even received a refund (Antonio will clearly explain the refund policy) for the one day that I was sick and couldn't dive.
Carlos, the equipment man at the El Coz, will move your gear to the pier and RUN to meet the boat when you return (he WILL be there with his dolly before you dock- through thick sand), and take your gear back to the shop, rinse and store it until the next dive when he repeats. He works hard for his tips and is worth every penny. No loading up gear and lugging it into a cab, etc., struggling with bags to get to a downtown dive op was really nice.
The dives were, as stated in previous posts, within conservative guidelines. Our dive group consisted of one very experienced diver, one moderately, and 3 beginner divers with only a few previous blue water dives. The conservative (50-60 ft usually),yet AWESOME dives that we went on were perfect for the experience level of our group, yet very thrilling for us all. Be sure and do Palancar Horseshoe. We had the same DM for every dive, and he did not babysit us. He and the boat captain both were friendly and professional. And none of us ended up injured or had any issues, other than we had to go home too soon. BTW, our boat did pick us up at El Coz for our afternoon dives, but perhaps it was because we had hired our own boat.
El Coz is very nice- the beds are hard but the rooms and grounds are spacious and beautiful. You will also be impressed with that mini golf course, it's really very nice. Play at night, much cooler and it's well-lighted. Food- some found it monotonous, I've gotten used to Caribbean food and appreciate it more now than I used to. The staff are very friendly for the most part, and will become familiar to you, as they work from daylight to dark.
Hope this helps. I think you will be happy with Scubadu, hope I don't give you a bum steer. But their convenience/price/efficiency/etc. made our dive trip an extremely pleasant one. Have a great trip!