I was looking at the evolution list for Eidolon today and something just didn't seem right with the Weapon training ability. Then it hit me that all non-native outsiders are automatically proficient with all simple and martial weapons. So why buy the ability to use martial weapons for evolution points? Is it just a trap for summoners without a beastiary? (honestly by the rules in the beastiary if you describe it as wearing full plate and using a double bladed sword your eidolon is proficient, which seems to take the inconvenience of armor training being eratta'd away, away) But perhaps I'm reading too much into all of this. Just hope my point that outsiders are automatically martial weapon approved makes it to the developers.
Already been covered somewhere in one of the questions threads. Eidolons do not start with any weapon or armor proficiencies. They also don't have all good saves like normal Outsiders do.