Although not as well known as some posts, this Shimano produced Pro Tharsis dropper is an amazing choice in the internal 27.2 mm category. I've been running a similar post for a few winter seasons on the fatbike and it's worked flawlessly.
Pairs well with the awesome and under rated and well priced Shimano Dropper lever. (Does not come with a lever). Also, the box for the post is missing/not included.