Seems powerful, but for developers only

The plugin itself seems powerful. However I wouldn’t know because it’s very difficult to use unless you’re a developer.

Be aware that there is no UI with this plugin, it adds a capability to your site but you have to handle code to use it. The documentation is written for developers. Even if you’re willing to learn, the doc provides little examples; mostly short snippets that you must know where and how to use. To top it all, the support team answers novice questions mainly by redirecting to the documentation, and make it clear that they’re not willing to help you below a certain developing skill level. So unless 1) you’re a developer, 2) you are willing to hire one to use this plugin, or 3) you use a page builder that integrates with Metabox and MB Relationships specifically (Oxygen for example), I suggest you pass.

Nothing wrong with making plugins for developers only, it’s a design and business decision by Metabox. But the plugin presentation makes it seem fairly beginner-friendly. It is not, you should be aware of it.