Is this the only Sandy left in the U.S ?

That's a yes

Yes

Locally owned since the 1940's with a 100 year lease I've been going there for 50 years Best burgers & custard in Austin.

This is a local grown place. Not affiliated with any other place.

Yes and the Best

This is no relation to the Sandy's chain (a McD clone) bought out by Hardee's years ago. It's a one off stand from 1945.

It is a different Sandy from what you may have experienced as a burger restaurant