Currently, Beautiful Taxonomy Filters does not support selecting multiple terms from the same taxonomy. This feature is on the roadmap. The plugin author notes that he hopes to support this in a future release and have beautiful permalinks. If the permalinks don’t work out, he plans to add an option where you can opt out of pretty permalinks in order to gain the power of multiple terms filtering.
Beautiful Taxonomy Filters does not support the built-in “post” post type. This is because de Jong has not yet been able to create proper rewrite rules for the multiple filtering to work, due to the fact that they are handled differently by WordPress than other CPTs. If you’re looking for filtering on regular posts, you’ll need to build that yourself, as it’s not included.