Assume I transfer my H1 to company A and if in a week or 2, I get an offer from a really good company, what are my chances of having a successful transfer ?
I said based on the experience of people I know. You can give it a shot. If you switch before the approval and get a denial later, you are totally screwed in US.
You should be fine to switch. Just don't take unnecessary risk of switching on receipt, always wait for approval.
Is the first transfer complete? As in approved and physical i797 in your hands? If yes, I see no issue. If no, the approval of the second will also depend on the approval of the first. If the first gets denied, the second is invalid/denied. If the first is approved, a denial of the second is not fatal, you still have the first.
Not much.
Is there a window defined like a month or 2 that I have to wait to transfer to the other company ? I just am not getting why it would get rejected. Both companies would be in the same field I did my masters in.