CMB2 is an excellent solution with outstanding developers, great docs and a great api and I use it a lot.

The thing is, CMB2, is meant to save time. While it is fantastic, it gives you an OK end-result that just works (which is incredibly valuable). I think if your product is about providing a UI, you have to strive to deliver an excellent end-result imo. And you can't really do that on top of CMB2, unless you're making drastic changes or forking the project.

For example, CMB2 has OK styling and design, but it's not fantastic and you don't have a lot of options on that end. It has incredible flexibility on the PHP end, but it doesn't let you do a lot of clientside operations, like advanced conditional logic that doesn't require a page refresh. You can tack that on of course like an add-on, but it's not part of the core API.

So CMB2 is such a big value add as a developer who just needs to plumb in a decent user interface with a lot of functionality and good API and do all that without reinventing the wheel. But if you want your UI to really shine, to be exceptional, it falls short. And that's not a knock on CMB2. But from a paid UI generator my expectations would be higher than just OK. And if you center your product around it, you also inherit its limitations.