Really... its a hard question to answer definatively. Depending on the size if the vase, the size of the betta, the frequency of water changes, the temperature of the room, the feeding habits, etc.
Is a vase ideal for a betta? No.
Do I want people to buy 'Betta Vases', No.
Why? Because a vase is a decoration, and most new owners have no idea about water changes and proper nutrition.
Also, most mass-promoters of betta vases used to do the same with goldfish first, but they died more quickly (no oxygene in water whereas bettas can breath from the surface).
I've seen really nice betta's in vases, and I've seen some really sick ones also.
In my world, each betta would have a 5 gallon, planted, heated, slow-filtered tank.
In reality, so long as they are treated humanely, properly fed and kept clean, that is all I can hope for.