Jet Boat Tours

I was leaning towards a form of a jet boat excursion http://phuketyok-travel.com/application/ ...
or
amphibious duck http://buyaduck.com/hybrids.html.
Given the age and general interest, would you suggest one of those two towers or something else that is promising and profitable?

I would not agree with you. There is little novelty in these two activities that are available everywhere. Personally, I do not like noisy engines polluting the beach, or what I can have fun riding. But pedal are nice .. serene, calm, promotes conversation and you get a workout from it. How not to try something historic, like a sailboat Bugis? You can even hire someone to play guitar and sing folk songs or local offer tea and snacks on board. If you do it well, it can become a "must" in everyone's itinerary vacation Langkawi, such as felucca in Egypt trip and a dhow cruise in the Persian Gulf.