turn and slip is certifiable where located I dont see what difference there is if you put an AI in the same hole instead of the T and S? It essentailly does the same job - just better
The AI and T&S are not capable of doing each other's jobs. Their gyroscopes are oriented on different planes, and each not capable of sensing motion in the other's sensative axis.
You will get varying opinons as to which is the preferred instrument to fly with, if you only have the one gyro. I certainly don't discount the turn and bank for getting you where you planned to go, in the absense of all other gyro instruments.
I flew an MD500 helicopter 1900 miles across Alaska and British Columbia. It had no gyro instruments. It was the T&B I felt I missed the most.