Beacious, I have my betta in a 7
gal bowfront with a Penguin Biowheel mini filter and a 50 W heater. He really does not have any problems with the filter turbulence. Like CiRXSi suggested, he simply stays to one side if he doesn't feel like getting a workout.
However, I am thinking of moving the betta to a standard tank with a sponge filter.
First, I am considering getting a few more bettas and for that, I would need a bigger, divided tank.
Also, I don't think that the bowfront tank showcases the betta very well. The distorted view makes small fish like corys look cool, but its effect on the betta is not very flattering. In addition, the top frame is pretty wide and unless I were to keep the water level very low, I don't see as much of the betta as I would like. You would probably run into these same problems with the Eclipse tanks - just something to keep in mind.
I would go with a standard 5.5
gal or even a 10
gal if you have the room - they are cheaper and will allow you to keep two bettas in a divided tank. Bettas are like popcorn - you can't just have one.
Do get a heater - even a 25W. A sponge filter will work just as well as a biowheel for less than half the price.
HTH