Plate Mail

Plate Mail is common Armor-class bodywear available throughout the Golden Sun series.

Basic Description by Game
Plate Mail increases the equipped Adept's base Defense rating by 33 points. As a common item, it can be bought repeatedly from vendors for 4400 coins each and sold for 3300 coins each.

In Golden Sun, it is sold in armor vendors at Lunpa, and can be equipped by Isaac and Garet. In Golden Sun: The Lost Age, it is sold in Champa and can be equipped by Felix and Piers. In Golden Sun: Dark Dawn, it is sold in Saha Town, and can be equipped by Matthew, Tyrell, and Eoleo.

Analysis
In Golden Sun, Plate Mails become available in Lunpa, by which time players could have freely won Spirit Armors at Tolbi with their Lucky Medals. While a Plate Mail has a single extra defense point over a Spirit Armor, a Spirit Armor adds 15 to all four elemental resistances to the Adept it's equipped on, which easily makes Spirit Armor better at lowering damage than a Plate Mail by a fair margin. For this reason, an Adept equipped with Spirit Armor should keep it on even when he is able to buy the strongest common Armor later on, Steel Armor, at Lalivero. And even if one of your Adepts is not equipped with a Spirit Armor, instead having an Armored Shell, a Plate Mail is still not a recommended buy (unless you have money to burn), because it is only a very slight incremental increase in defense.

In Golden Sun: The Lost Age, the Plate Mail has far better potential to be very useful and worth your money. When you get the Lemurian Ship, the entire Great Eastern Sea and the many settlements located throughout it open up for you to explore, meaning the Plate Mail can be bought at the seaside town of Champa as soon as you set out. At that early point, it is a strong replacement for any Psynergy Armor your party members might be equipped with, and the Plate Mail might actually remain on your party for quite a while because, in comparison to other classes of equipment in The Lost Age, strong bodywear artifacts are surprisingly rare to come by until when the Great Eastern Sea segment ends at Lemuria. Namely, unless you forge Planet Armor from Star Dust at the blacksmith in Yallam, the only armor that can effectively replace a Plate Mail is the Phantasmal Mail found deeper in Izumo Ruins.

In Golden Sun: Dark Dawn, Plate Mail is even less useful than in the first game. From the moment they become available, they are completely outclassed by the Spiked Armor that can be found earlier in Craggy Peak Ruins and by the Planet Armor that becomes available in Port Rago at the same time as Plate Mail can be bought in Saha, and between these two, both warrior Adepts can be equipped with better armor. Therefore, ideally, Plate Mail would never be useful.