Backstory:
Mitch made SkeletonUtility for Spine-Unity and built it on top of the old BoneComponent.
The functionality changed so much that he just removed the old BoneComponent.
But knowing what the old BoneComponent did was still useful for simple cases, he left BoneFollower.
(1) So yes, BoneFollower is what used to be BoneComponent.
Nothing tk2D specific there.
Rendering (and everything dependent on it, atlasing, attachment stuff) is what makes Spine-Unity and Spine-TK2D different from each other.
BoneFollower (or the old BoneComponent) doesn't use any of that stuff. Just Skeleton and Bone.