I have tried sportsbet, nitrogen, cloudbet,stake, and even bitcoinrush they are almost similar and among these sprotsbook, sportsbet and stake has bigger markets based on my own evaluation.
not really , most of them have different providers , but I think there are only three in total that they are all using
the odds could be very close but definitely different - if you think that 1.83 3.05 1.9 and 1.8 3.10 1.95 , for example are almost same odds , you are mistaken
the main thing is what margin the sportsbook is taking and what are the odds initially