SquidMarks, you have a good eye. Alan Hawk stated that Shimano Thunnus Ci4 was the best of baitrunners in his 2015 blog (http://www.alanhawk.com/blog/wr15.html) while Shimano Baitrunner D was the second best one at almost half price of Thunnus Ci4. The extract is below.
"Free-lining reels
These are the reels commonly known as "bait-runner" reels due to the popularity of Shimano's Baitrunner model, lending its name to the entire category.
This is going to be a simple one; the best one available by a clear margin is the Thunnus CI4 which comes with tougher gearing than other mainstream free-lining reels, in addition to a highly reliable mechanism and excellent build quality. The second best would be Shimano's Baitrunner D, but I really recommend spending the extra and going for the Thunnus CI4. You don't need to look beyond those two reels. There are others that work fine, but there isn't a compelling reason to buy any unless you were after certain ergonomics specific to another reel"