Hey man, I'm not forcing this dude into buying a single fin - it is simply a suggestion based on my personal experience. Nothing about the OP's post insinuates that he is a beginner - the only thing we know is that he is considering a 6'6" - obviously not a typical beginner board. By all means, a funboard is a lot of fun - I have one myself, but I think we can all agree that a funboard will not yield the same results as a 6'6". Sure, a single fin is not a thruster & it's the same vice versa. A thruster is a combination of a twin & a single, but it still lacks the stability of a single fin. Additionally, a thruster has a lot of drag - something that may complicate things for a beginner. A single fin set-up provides a smoother ride & offers more stability than a thruster does, with little-to-no drag. From a historical point of view, the single fin is the original - the classic - the mac daddy of fin set-ups. The single fin allows the rider to go with the flow & ride the wave for what it really is. If the OP is really a beginner, the single fin will teach him style & finesse of true classic surfing. From there, you can go anywhere; including a thruster set up or even a quad set-up - you could even look at single fins as the "stick-shift" of surfboards. Style & grace over airs & modernization - restore the power.
Just read a great article in Surfing Mag the other day about single fins. It basically talks about using a single fin when the conditions are clean with long rides, to get the most out of it and when it's bumpy / semi bumpy it's best to use a thruster. Guys like Kelly and Dane love the feel of a single fin when the conditions are right but i'm sure it's fun to surf in lesser conditions too. It says it will force you to pay attention to certain things and therefore improve your surfing overall when you try different equipment. Many will say any complete quiver will have a single fin in it. Just my .02