The 120mg format does the math for shared use - if you and your wife are both at 8mg every 4 days, that's roughly 4mg/day combined, so a 120mg vial gives about 30 days of shared stock. The tradeoff is more risk if it degrades or gets contaminated, so BAC water and cold storage matter more at that scale. Reconstitution concentration needs recalculating versus standard vials to keep draw volumes reasonable.