Hi Nikhil,
I am working for one of the Citigroup companies and on the project on which Iam its being developed by polaris pretty huge one. Apart from this there are lots of other citigroup projects which are undertaken by Polaris.
Given that Polaris's main business is from citigroup their domain of specialisation is Banking and Finance if you are looking to switch to banking domain I think it will be good company to go for.
As far as on site opportunity goes I don't know about Polaris Mumbai but from Polaris Chennai I have seen people moving to on-site support especially the project on which Iam.
Cheers