Just some friendly feedback, I hope you don't mind? I've used your plugin a few times in the past and it's worked great. I just installed it again on a client site and noticed it now shares the built-in tags/categories used by posts. I guess this is new as I don't recall it sharing these in the past.
Anyway, I haven't found a problem or anything, but it just struck me as strange it shares the default tags/categories, surely custom taxonomies for your custom post type would be the way to go?
Many themes list blog/news categories in sidebars, whereas now it would also list your testimonial categories. Another use case - I've built many sites where the post archive page has filter buttons dynamically generated from the post category names. Again your testimonial categories would show on the news archive pages in this instance.
It would be possible of course to exclude your testimonial categories by ID in custom code, but this wouldn't be easy to maintain if new testimonial categories are added.
It just seems to me that the built-in categories/tags (that are mostly used for posts for most WP sites) are sufficiently distinct enough from the testimonials to warrant custom testimonial taxonomies?
Not a criticism, just feedback - I don't think my coding skills are up to your standards to help you out by contributing code, but I'm happy to beta test any changes or provide feedback to help you improve it.
Also, I'm always amazed at how much time and effort people like yourself give back to the community, so thanks for your time and efforts :)