What I don't get in this system is that the first aid critical fail rate doesn't depend on your FA skill at all.
You always have a chance to critical fail 5% times - your luck is checked, if the Luck roll fails it's critical fail.
So person with 300% FA and 1 luck has exactly as many "horrible first aids" as a person with 30% FA and 1 luck. And it has more critical fails than a person with 30% FA and 2 luck... It makes luck skill too important for medics IMO.