Julie, our guide was great, but the kayaking was rough. I've asked for tandem in the comments, but that was overlooked, so we all got single kayaks (I have an 8 and a 12 year olds). Luckily one couple agreed to split (otherwise had to reschedule which was not an option), so I could do tandem with my 8 y/o, but my wife and 12 y/o had to do single. It was a difficult 2 hour kayaking against gusts and with lots of boat traffic, and 30 min with the manatees. On the way back the guide connected my daughter's kayak with a rope to help her. As for the manatees - you can barely see them because the water is not clear. You can see the same by parking at the spring and seeing them.
A couple years ago we did a similar kayaking tour in Crystal Springs (a 1.5 hour drive north), and it was so much better. Clear water, short and easy paddle and a much better facility. No boats and lots of manatees that you clearly see from your kayak.
Overall, if you're in the area, and have strong kayaking abilities - it's fine. The guide said I should have booked the tandem tour, but I couldn't find it. Also, there's no option to mix tandem and single, and I assumed that they read the comments before hand. Also, probably best to call them directly and say exactly what you need. And get ready for a workout. Tarpon Springs is a cute town, dominated by Greeks, which is like being in a greek village. Very fun.