Fighters are easy to keep but very prone to being nipped as well as nipping themselves. I wouldn't place him in with an RTBS, and the tetras you mentioned in the other thread are a questionable tank mate

. Community tanks and Bettas (fighters) is a grey area of the hobby ATM. Many have tryed it and had it work, like me

. Others have tryed it and found it to end with the death of the fighter or the current tank mates and on occasion some tank mates and the betta

.
You would be best asking about them in the Betta area of the forum, where some of the more experienced Betta keepers can help you
All the best
Rabbut