In the Halmos scheme any linear bijection between B a vector space and its dual establishes a quadratic form Q. For x and y in V, Q(x, y) = B(y)(x). (B(y) is in V* and is thus a function with V as its domain.)
There is something else significant: the Dirac vision exploits an automorphism in the complex numbers. The book introduces the notation “⟨A|z” without explanation. Does the “A” within “⟨A|” denote something as “2” within “2+4” denotes two? Which one is the vector? What does it mean to write a vector, ⟨A|, to the left of a field element z? The equation “⟨A|z = z*⟨A|” seems to me to be a definition of notation rather than an axiom. In general the fields of many other vector spaces have either no automorphisms, or many.
I think that the book does not follow thru on the promise to distinguish between a vector space and its dual, or as they would say a bra and a ket vector. That’s OK for there is a natural 1-1 bijection between them.