Strengthless casters, don't hold your breath. While the Summoner's Leather boasts very impressive boosts to intelligence, willpower, and MP, it is still leather armor and requires just as much strength to use as standard leather. While there isn't necessarily stopping any character from shelling out stat points to get 20 strength, many people prefer simply to put more into their respective casting stat and hunt for low-strength armor with good bonuses.
Dropped by Eclipses, the Summoner's Leather probably sees the most use in combat characters with MP-intensive spells such as Teleport. Its damage reduction is only slightly lower than standard leather, and while it can be used in a fight, the expense of repairing it can be quite a burden.
Stats[]
Weight: 8 | Level requirement: 45 | Strength requirement: 20
Damage reduction (armor): 10
MP: +10
Int: +5
Wil: +4
Poison resistance: -6%