It's been more than a year since I've had a Thai banana. I believe they go by the name of Nam Wah. I remember it as being sweet with slightly sour/vanilla overtones. They are firmer than the more popular/common Cavendish banana, and should be showing some black to indicate ripeness.
https://www.youtube.com/watch?v=8R64M22Pt50&t=22s
I like them more than the Cavendish ... more character. I understand that they are often served fried, but don'thave first hand knowledge of that.