The main advantage I see is that sodium borohydride, as a liquid, can be stored in the wings. Liquid hydrogen storage is dictated by the spherical or cylindrical shape of the cryogenic tank. You can't store liquid hydrogen in wings because the surface area-to-volume ratio is too large, allowing heat transfer and boil-off to occur too rapidly. Sodium borohydride stored in wings could therefore permit greater aerodynamic efficiency and cargo capacity for a hydrogen-fuelled aircraft. I don't think it could compete with aviation fuel in terms of raw efficiency, however the aircraft would be transformed from an ignitable flying bomb into something far less useful as a weapon of terrorists.

I would recommend liquid sodium borohydride fuelling for all the largest aircraft - the ones that could be used such as they were on Sept. 11th, 2001.