I do think my betta really enjoys the Spec. It's true they're not the best because they are small and mostly vertical space. They might be better for plakat or female bettas since long fins might get blown around or caught in the overflow. My betta's favorite thing in the world is resting against the overflow. I can see him hanging out there right now! I would love to get him a Mini M but that'll have to wait :P
You'll probably have to do some mods since the filter is so strong. I turned the filter down to low and stuffed the overflow area with filter floss. That lowered the flow enough for my plakat, but for a long finned you might want to cut some slits in the return hose. I also had to pull my hardscape out because my betta kept wedging himself behind the rocks and I was paranoid he was going to end up getting hurt or stuck and drown
