I think you have to say something about the copy semantics too, because if you ignore those, value_ptr would be synonymous with unique_ptr.

   class Tree { Tree *_left, *_right; };
   Tree y = x;

makes a shallow copy.

   class Tree { unique_ptr<Tree> _left, _right; };
   Tree y = x;

doesn't compile, but

   class Tree { value_ptr<Tree> _left, _right; };
   Tree y = x;

makes a deep copy.