Background: I paddled whitewater in southern Virginia and for a few years in Minnesota. I still paddle canoes, but I'm a wimp about cold water and the rivers in Minnesota mostly only run in the Spring when they are freezing, so I don't paddle whitewater any more. Now I canoe and occasionally paddle flatwater kayaks, but I like canoes better on flatwater. I sold canoes and kayaks at Midwest Mountaineering for five years, which also involved a lot of boat demos.
If you are planning on doing a lot of flat water, you don't want a whitewater kayak like the Fun or Fuse. If you are planning on doing a lot of white water, you don't want a flatwater kayak. There really isn't a great crossover option because the qualities that make a good whitewater kayak are precisely the opposite qualities of a good flatwater kayak. Any crossover is necessarily a study in compromises.
That said, many kayak manufacturers do make crossover kayaks that are basically flatwater kayaks with a bit less of a keel than a true touring kayak. Those with more rounded hulls often have drop skegs so you can track straight on flat water but still turn (enough) in moving water.
If you intend to limit yourself to fairly light Class I and II rapids, you will probably be happy enough with a crossover like the Dagger Axis or Katana. I was fan of the old Dagger Blackwater, and these might have inherited some of its flexibility (or you could look for a Blackwater at garage sales or on Craigslist).
Finally, whitewater kayaks don't really progress with you. When you start, buy a cheap used kayak. It will take a season or two for you to understand what you really want. And you'll probably only own that kayak for another year or two before you want something else. Plus, most whitewater kayakers own at least two or three kayaks because they don't all work for all rivers. Like I said above, kayaks are very purpose-built.
Sometimes you want to play in a hole or on a wave, so you want something short and stubby that surfs well. Sometimes you want to run big water and stop for lunch in the middle. So you need a longer boat with some volume in it. When the water is up, you want to bash down a creek, so you need a creek boat.
It's an expensive hobby, but fun as hell.