1st thing here: it's kinda unintuitive that it says "no options" in the drop down, my first impulse is to assume something is wrong/unavailable and to skip this point. The name we typed in to the title of the book should be prefilled OR, there should bean option to prefill with the name, AND/OR there should be some explanatory text that says: "type in names of works you wish to add or link (or paste bbids)" or similar.

The box for adding a work is too narrow, there is a lot of extra horizontal space going to waste (also I maintain that most of this could be in boxes on the page and popup be be only for extra details like identifiers, etc)

Speaking of, there is no reason that these boxes are collapsed and need to be expanded

Finally to an issue here, in the entity link box, author credit, everywhere like this, searching for a name (here author) will only show the name like so, no aliases or sortnames. There is a "look up" link icon on the name, but if clicking that (and when the same bit of popup is actually used to select for the entity, it's.. unclear and kinda flimsy that this is the thing to "lookit up" on)
Anyway looking it up on another page/tab (again it's not a link, so left clicking or ctrl clicking does nothing)
It does open the page but when we return to the tab to select the name it has disappeared so we must write it again.

And now again to adding a relationship, which it seems the book part does not have?
I added the book with it's work and author, but had to open the conventional edition edit screen to add relationships.

And here is the issue there: typing in a name that does not exist does not show a link to "create entity" which I would expect, nor is there any informational text on how to do that, especially after the book-adding routine.

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This has been my first attempt at actually adding a real work with the finished unified form routine. it's got Great Potential!
But it still needs quite a lot of work before it is "production ready" I'd say.