PGCGM is an excellent course if you want an IIM certification but don't want to leave your job. The learning is the same, and the faculty is the same; the only difference is that this is taught in a virtual online classroom rather than you sitting in a classroom in Calcutta. It also includes three campus visits, so you can get a feel for the campus.
Most people struggle to get into an IIM, and the PGCGM course costs 3.5 lakh versus 31 lakh for ISB's PGP Pro course.