Rated 1 out of 5 stars

Cannot choose specific destination folder.

This review is for a previous version of the add-on (1.4.3). 

Versions of Extract 'Em! prior to 1.5.1 deferred to the Thunderbird settings for FIle and Attachment handling (always prompt or use a specified directory); I suspect that your setting was for the latter. With 1.5.1, an Extract 'Em! option has been added allowing you to select whether you want to be prompted to select a directory, or always use the one indicated by the respective Thunderbird setting.