VocabJuice was developed because I've found that Kindle Vocabulary Builder to glitchy and not convenient for use.

I ended up developing an application that exports all the words I checked to my mobile and desktop devices and convert to flashcard for an efficient memorisation. I'm now testing it, hope to upload it to the web by the end of the month. Check it out and leave there your contact details if you want me to notify you once it up. https://vocabjuice.com/