blind or partly blind bettas, in my personal experience with Theo, are no different than bettas that can see, except they're a touch more skittish and don't flare nearly as often. i often see Theo swimming about his tank, but he prefers to chill and 'walk' on the bottom, and will zoom up to his big pink plant the moment anything happens(like if someone stomps in the living room, drops something heavy, comes through the front door, ect. anything that causes vibrations).
so, if you find a betta you like, or even one you don't really like, and it's blind, get it. :p honestly, i'd rather someone on here get a blind betta, than someone who knows jack and will shove the poor thing in a vase/too small tank. i'd gladly adopt another blind betta. :3