Yes, it seems to work well. I'm attaching what I see in the header in the web viewer. It shows first a local number based on the size of the page you're watching and then the "real" page number and the number of pages.

https://s3.amazonaws.com/zotero.org/images/forums/u1102525/bik1kxze17824235518w.png

If you come across ebooks that show physical page numbers in Calibre but don't in Zotero, please report them in a new thread. (There's a standard way to mark physical page numbers in EPUBs, but few EPUBs actually use it, so the best we can do is use heuristics.)

Re toolbar display, it's actually the other way around. The physical page number shows in the text box on the left, and the "logical" page number shows on the right. You can hover over the text box on the left to see whether the page numbers map to physical pages - if they do, the tooltip will say "Page", and if they don't, it'll say "Location".

This is not ideal UI. We're working on improving it.

https://www.w3.org/TR/epub-33/#sec-nav-pagelist

https://www.w3.org/TR/epub-ssv-11/#pagebreak

There's supposed to be a <nav epub:type="page-list"> element in the nav document, with corresponding <some-tag epub:type="pagebreak" title="123"> elements in the book's text. Zotero only parses the latter right now.

Most EPUBs with physical page numbers that I've worked with have done it their own way - usually something like <h1 id="page123"> in the text.