I've been evaluating your software and there is just one issue that is a deal-breaker. There should be more specific control over the Guest Access Rights. I need a guest to have the ability to comment and upload attachments on cards. Here are just 2 examples where this would be useful; a client can answer a question from a developer or upload a screenshot of a bug. If a guest is a collaborator, they can disrupt workflow as they can change/delete cards on boards, mark complete, move to different lanes. Not good, not good at all.
This is just a suggestion for others who come after me that needs the same. I need software very soon and so I will be moving on to evaluate other tools.