What's an "amagat"? How is it different from the Loschmidt Number?
I haven't seen any of these particular units before so I could be mistaken, but I imagine it is similar to how we don't say "I have 3 Avogadro's Numbers of water" we would say "I have 3 moles of water". We very well could describe amounts by explicitly naming multiples of the constant, but we instead defined a new unit so that we could describe things more easily.