I hope you don't mind me butting in on this but I just don't understand any of it. Is this new ACBF Viewer an alternative to, say, Perfect Viewer or Sequential Image Display? If so, what does it do that PV doesn't. Also, I haven't a clue about "metadata". For the most part, most comics I read, I will know, or be able to quickly find out, writer, artist, publisher details. I know you talk about panel by panel viewing and have to ask what is so new about that? I can zoom in on any panel in a comic as it is.
I have a feeling I'm missing something here but don't know what it is. It's like having a car, I can drive the thing but what goes on under the bonnet is for a mechanic to know. I just want it to work when I need it.
With metada you can search through your library quickly and find particular comics and start reading them. When you import a comic book into library in ACBF viewer, it imports all the metadata with it (authors, genres, series, publisher, publish date, story description ...) as all this metadata is embedded in the comic archive itself. You can see the screenshots from viewer and its library
here to get an idea. It is even capable of creating different statistics and nice charts on the library metadata.
Regarding panel by panel viewing, when panels are defined, you don't have to zoom in manually, the viewer knows where the panel is and zooms in there. It's like "guided view" in I think Comixology they call it like that. It's better to try it, it's harder to describe. But for this I recommend Android viewer as it can smoothly animate between panels.
Another feature is to have a table of contents (you give particular pages a title). I often have bigger files containing the whole volume of particular comic and with table of contents you can quickly jump to particular issue or just see what is inside.
Another feature is text-layers with translations to different languages, you can switch between, but that might not interest you.
ACBF viewer makes use of all these metadata but you can still read the comics with it even if they don't have those.