Yes, the fruit from India and what we have here do look totally different. Some day, we will know what our "Himsagar" actually is.
The original fruit is from West Bengal in India but it is not sold much at all in any other part of the country. According to a friend of mine from Kolkota, it is the favorite mango for most people in the state. They love it so much that people in other states do not get to taste it.
I have a Himsagar tree and have topworked it to two of my trees (Keitt and NDM #4). I got fruits off the topworked portion of my Keitt last year. Really good, but not in the top tier, at least for me. It is, however, very productive. Zills describes it as "very productive."