So I tried it just now. I set the plugin first to create collections for the custom column and the series. Once it's done, I got 398 collections. I then imported the Kindle collections to Calibre. Everything looks good.
I then set the plugin to create collections only from the Imported Kindle Collections column. When I clicked on preview though, it generated 619 collections, which is way more than the number of created collections of the series + finished books. The report says that the collections were created from the Imported Kindle Collections column + other (no idea what the "other" refers to, though).
To be on the safe side, I'll probably just set the plugin to create collections from series and the Custom Column and manually tick the Finished Books column in Calibre. But I'll use the Import Collections from Calibre plugin as backup.
No regrets jailbreaking my Kindle for this awesome plugin. Thanks for all the hard work, NiLuJe!
