Never heard of Migrate Me so no idea how well it migrates 3rd party extensions. Core Joomla usually migrates fine, but 3rd party extensions are either ignored or the Joomla user ID was changing causing 3rd party DBs to go out of sync. I know users have had success with SP Upgrade.
If migration works well and the user ids are not changed you'll then need to go through all of CB and correct the View Access Levels and Usergroups to J3.x values. Your Joomla 2.5 install isn't a migration though, just upgrade to J3.x after installing CB 1.9.1.