I'm not going to make any claims about authenticity or the like. I've never been to South India. I do know that lots of people come here when visiting the big temple nearby, and some of them say it's authentic,but whatever.
What I do know is that it's delicious and inexpensive. I'm not usually a fan of vegetarian cuisines, but this place is terrific.
If you're like me, you're going to look at the menu and realize you're stuck. All the "Indian food" standards you know are absent, and there's a huge amount you've never heard of. What to do?
Under "Chef's Specials," there are two meals. One has dosa and idli, and the other is a thali with rice. Decide whether you want more or less starch, and then pick the meal accordingly. $10 later you will be full, you'll have tried a lot of things, and you'll be planning to come back.
Oh: if you can't tolerate spice at all, skip this place, because they basically go from "a little spicy" to "holy XXX".