I brought the original Edge 6 gallon when it came out and was introduced to this wonderful hobby. The very first fish introduced to the tank was my blue betta.
The fish store had a display model with 1 betta and several other fishes, they recommended the betta as a good choice for a beginner.
It was awful watching him struggle at the top, he would dart up constantly around the hole. Sometimes he would get lucky and find the hole, other times I would watch him slowly drift down to the bottom. I think the lack of air is stressful, maybe not deadly but defiantly stressful.
My sister has her own betta fish in a 10 gallon and his behaviour is a lot more pleasant to watch. They like to sit on top of plant leaves and float up for air. Mine had to swim for a while before reaching the hole, which sometimes doesn't happen.
The final straw was watching him sleep (or rest?) then drift up for air, only to find an invisible wall. It was an awful sight and I couldn't enjoy my tank.
Beside the fact that it took him a while to find the hole, I saw him flare with his reflection. The side panels of the Edge are mirrors (if view within), this caused him to flare quite a bit. A frontal view of the Edge reveals a two sided mirror, these mirrors at both sides give a 3D effect. I'm not sure if it's healthy for a Betta to constantly see his reflection.
After a week, I decide to fork out a few bucks for his own tank. I'm sure there are people who successfully house a betta fish, I guess it all depends on how smart your fish is.
Maybe I should of waited more than a week but I couldn't stand watching him dart around the top glass.