There is a bug I noticed with importing contacts on Runbox 7 - custom fields (e.g. choosing your own label instead of Home/Work/etc for emails, phone numbers, etc in contacts, you can do this on Android) are not preserved when importing them using Runbox 7. It is possible to import them using Thunderbird or create them with any CardDAV client but Runbox 7 will change the custom field to “Other” with no warning or error.
Another thing that prevents me from using Runbox’s contacts is the lack of a birthday calendar that automatically populates with the birthdays of people saved in your contacts. It would be really nice if Runbox could implement these features 