Having handled hydrogen gas
Having handled hydrogen gas personally and having held a Hazardous Materials license to haul it, I can say that your impressions of hydrogen gas are largely incorrect. It's NOT safer to transport or pump. In fact, it's the least safe of the flammable gases to handle. Especially under pressure. In a crash, it doesn't "dissipate into the air" it EXPLODES into the air in a fireball.
Did I mention that hydrazine hydrate doesn't require expensive compressors or handling equipment either?