I completely disagree. The betta will be fine in the jar. And i am looking at only getting one male betta for the ten gallon and some neon tetras and maybe a zebra dion.
The goldfish were fine! They were better off than they were before in a bowl and they lived out the rest of their lives healthy and happy!
We've told you. Neon Tetra's and Zebra Danio's are too big for the 10 gallon. You'd only be able to have Forktail Rainbowfish, Ember Tetra's or Galaxy Rabsoras in the 10 gallon with your male Betta.
NCGuppy: I've noticed a difference in betta's kept with smaller surface area's.
As for the goldfish, they were stunted and in pain. Simple as. They may have lived another 3 years in the tank but they were probably only about 1-3 years old before your neighbour got them anyway which means they still died young when they could have lived to over 30 years in the correct conditions.