Sadly I haven’t found a solution yet, just having the same issue trying to switch from other mailing software. Did you find a way to implement the custom boolean field on the preferences page? I only found this suggestion.
Another problem I noticed: We have multiple types of users and they don’t need to see every segment that’s set to public. At the moment I can only set them to public for everyone and users could subscribe to a segment that doesn’t matter to them at all.