Hello,
We did the stingrays with them last December and loved every minute of it. My husband did not realise till we got to their 'boat' that we would be travelling on a catamaran - far nicer than the crowded rust buckets we saw moored either side of it and out at the sand bar. They motored out to the sand bar - as we layed on the nets over the water and snoozed in the sun, then they sailed back - just perfect.
The two man crew were friendly and helpful and their photographer was nice too. As for stingrays - awesome!
We did the 9.30 trip, it was not hard to find their 'office', they will provide you with easy clear directions when you book the trip. Well worth the money - and far, far cheaper then booking onboard. They dropped us off in town afterwards, leaving lots of time to wander around, shop and eat.
Take disposable underwater cameras, we got great pictures of us and the rays - though we also paid for their pics too (you can see it on the digital screen before you decide) it was worth it we got a CD with the pics a few weeks later and the pics are really nice - clear and the color are really vibrant - a great screensaver!
Go for it - we are still talking about that idyllic day 6 months after the cruise and will probably do it again when we are there this December too.