12"+ is a lot of height in a tank. Bettas prefer long, shallow tanks as they do come to the top for air. Tall and narrow are less desired. There is such thing and too shallow, as well as too tall.
Anyways, I would use these as I have no issue with 3g tanks. AT ALL. I have seen members use these and have happy little fish. I also use the larger 25g Sterlite/Rubbermaid containers for lager tanks when needed. I like the 7g containers you posted as well, much more actually. But yes, I would use them, put a few glass rocks in the bottom to give it color and some nice plants. They do have small plants with suction cups on them, you could suction them to the side of the container on the first one you posted. Main thing is, can you heat them?