The Gold Stud is my personal favorite Accessory. The only real issue with it is that it overshadows almost every other Accessory in the game. It reduces all MP costs by 3/4, leaving the most expensive Techs in the game at a cost of 5 MP. With 99 MP total, these Techs become usable 15 more times before you need to restore your MP, which is quite significant. The only downside is that you don't get any bonuses to your actual per-Tech damage, so you won't see the benefit in the short term.