My wife and I flew down to Florida for a quick trip last weekend and did the manatee tour. We used Birds Underwater as well, and highly recommend them. Our guide, Donna, was great. We were one of the first boats to arrive at Three Sisters Spring, and some of the first people to swim into it, which gave us terrific viz. Most people stayed in the main open area within the spring, but we swam around to the left, and ended up with tons of great photo opportunitities. I had a strobe, which I was planning on using an hour after sunrise, per the new regs, but after one shot decided I was better off without it.
One note, for anyone considering this trip: if you're a cold water wimp and have your own 5+ mm wetsuit, bring it. The water is 72 degrees year round, and the wesuits that Bird gives you are 3mm. Everyone on our boat in a rented wetsuit was cold. I had a 5mm, which was fine (except for the water that kept going down my back), and my wife had a 7mm, which she said was pretty warm. Keep in mind that most of the time you're just floating there motionless, waiting for the mantees to surface/interact.
We stayed at the Holiday Inn Express a couple miles east of Bird's Underwater. Clean and inexpensive, and perhaps the most comfortable bed I've ever slept in, so I would definitely recommend it.
We thought it was going to be a pretty neat experience, but I have to say it completely exceeded all expectations.
Couple pics are attached.
James