I wanted to thank you for this great plugin. I installed it on my Windows 7 machine using Calibre 0.7.44 and plugin v 1.2. I had already created a custom tag "kindle" as text column to put the individual category name I wanted a book to show up under. I got things installed, ran it and everything worked cleanly from the first use. THANK YOU!
One note I wanted to make based on my usage and not sure it was clear from the instructions - when customizing the plugin and looking for custom columns, the plugin is only reading the books on device rather than what's in your library. I had completely cleared my Kindle and was "re-initializing" it so when I first plugged it in, I had none of my calibre managed books there and my custom column didn't show up as an available option to create collection from. Once I copied over my books and then went to customize, my custom column was there.