My question is a follow up to this one: Does the collision of a neutron and anti-neutron produce energy?.

Quoting from an answer:

"The collision of a neutron and antineutron star would initiate a terrible strong annihillation. The result would be similar to a supernova with an extreme gamma photon flash. It is hard to say, what would be the result. In the Universe, no significant amount of antimatter exists."

Let's say this is the smallest possible neutron star and smallest possible anti-neutron star. Sure, there would be an extreme gamma photon flash. But I want to know how devastating this will be. Will it destroy the entire galaxy with material spewed out into inter-galactic space? Or will it be like any other supernova explosion? And will this result in a black hole or just a big explosion followed by nothing?