Something I've already noticed after having a Betta fish for only four days
Is that they are a lot smarter than goldfish. (Which I kept when I was a kid back in the late 1980s.) Betta fish don't eat everything and poop in the water and have their stomachs explode. Goldfish do.
I recently learned that goldfish are a lot harder to keep than people think. They are filthy. And my niece just got one.