Originally Posted by Goldenrod
I always get the no suitable format to unpack
The plugin only works with MOBIs and MOBI variants. EPUB, LIT, HTMLZ, LRF, PDF, PDB ... none of these formats are "suitable to unpack." That message just means no MOBI, AZW, AZW3, AZW4, or PRC format was found for that particular ebook in your calibre library.
If you deal primarily with ePub or other non-MOBI-ish formats, this plugin probably won't seem very handy to you.