Bombay needs some south indian spice and Dakshin's attempt is good. The ambience is a little over the top and the waiters are not wearing 'veshtis' but some other form of lungi which is not 'South Indian'.
The food is a little confused but it is probably the most authentic in a five star. I cannot say the same about the non vegetarian food because I did not try it. But the vegetarian fare is interesting. It is obviously expensive because of its location but there's no harm in trying it once.
All in all an average experience.