Chain Mail

A Chain Mail is an Armor-class bodywear available throughout the Golden Sun series.

Basic Description by game
Chain Mail increases the wearer's base Defense by 25 points. As a common item, it can be bought repeatedly from Vendors for 2000 coins each and sold for 1500 coins each.

It is sold in armor vendors at Altin and Kalay in Golden Sun, at Kibombo in Golden Sun: The Lost Age, and Te Rya Village in Golden Sun: Dark Dawn. Being an Armor-class piece of body protection, a Chain Mail can be equipped on warrior-style Adepts, namely Isaac and Garet in the first game, Felix and Piers in the second, and Matthew, Tyrell, and Eoleo in the third.

Analysis
In Golden Sun, Chain Mail is not a recommended purchase due to the fact that the player usually has access to more useful armor like the Psynergy Armor in Mercury Lighthouse and the Elven Shirt in Mogall Forest, whose additional effects more than make up for the fact they each have just a few Defense points less than a Chain Mail.

In Golden Sun: The Lost Age, Chain Mail can first be bought in Kibombo after the Gabomba Statue dungeon and related events. Out of the two warriors capable of equipping it, Piers will start with Chain Mail as his default bodywear, and Felix will be equipped with a Psynergy Armor bought much earlier at Mikasalla. A Psynergy Armor, quite frankly, is better than a Chain Mail even though its monetary value is literally half as much and it has a few less defense points, because it has a significant PP-meter boost that is very useful at that point in the game. It is possible Felix will have found the Ixion Mail in Alhafra before going to Kibombo, so if he has a spare unequipped Psynergy Armor in his inventory when he meets Piers it would be sound to replace Piers' Chain Mail with that armor as soon as the latter joins.

In Golden Sun: Dark Dawn, Chain Mail is certainly not a good purchase by that point in the game. In addition to Psynergy Armor being available already, even reaching that point in the game means passing through The Ouroboros, which contains the Ixion Mail, and Craggy Peak Ruins, in which chests contain an Armored Shell and Spiked Armor. Even if the higher Defense points compared to the Psynergy Armor are desired, those three armors all have even higher Defense than the Chain Mail, and two of them have their own beneficial effects on top of that. At the time, only two available characters can even be equipped with armor in the first place, so even if only two of the three are found, the Chain Mail is completely outclassed from the moment it becomes available, and therefore it should not see any use.