We booked the Go Flamingo tour the day before heading out. The staff at the shop were very friendly and helpful.
Our guide for the day was Gilberto (named for a hurricane!) and he was lovely. We (2 adults and 2 kids) shared the trip with grandparents from Mexico City who spoke no English. This added to the fun of the day as they were very taken with our youngest child and his silly voices.
The trip started with a light breakfast of pastries and coffee/tea in the office at 6:30am and then we jumped into the A/C van for the 1.5 hour ride to the sleepy village of Rio Lagartos. We went in low season so there was very little in the way of other tourist activity which was nice. We spent about 3.5 hours out on the boat looking for the flamingos (the first of which we spotted before stepping aboard). The only downside of this trip was that we'd left our own binoculars at the hostel as we'd been told that they had them. Unfortunately these were not great quality and found them difficult to use - so if an improvement is being looked for - replacing this would be the thing to do.
We stopped at the clay bath on the way back for lunch where the kids had a Lord of the Flies moment. You then jump back in the boat to go to an out door pool area which is sea/fresh water to rinse off before heading back to the village for lunch.
Lunch was nice- water is included but if you want beer/coke that's extra.
After lunch it was back in the van for the trip to Ek'Balam. The entrance fee was not included in the price of the tour but this is fairly common in the Yucatan. We had a Mayan guide for about 45 minutes then were left to our own devices for a further 30 minutes or so before heading back to the shop and a drink of Xtabentun - the Mayan version of Pernod but with honey - very very nice!
If we had more time it would have been nice to explore the other tour options that they had but the flamingos was one of our main reasons for going to Valladolid in the first place so mission accomplished - thanks Gilberto!