@Degs: Unfortunately, if you idle in a bow (e.g. Rosenbogen, Arco de Velocidad, Lamian Kaman), you will end up losing TP if you macro this in, making it pretty counter-productive. You'd have to idle in something like Happy Egg or Attar of Roses to keep it.
Prolly get rated down but here goes: 1 Enmity isn't really ground-breaking, but neither are any of the other ammo options for PLD. Hp, Mp, Vit, are all very meh.
Hp will more than likely never save you from dying, and in any other situation max hp means very little (except yellow hp for blood aggro or some such obscure scenario)
Max mp is useless after you get past the 10-12 you get from bow/ammo
2-4 VIT will rarely make a noticeable difference when being hit by just about anything.
Only decent stat on ammo i think is MDB, which can make a difference in some battles. Aumoniere should certainly not be looked down upon for ONLY offering 1 Enmity, in a lot of scenarios that's the best you can get.
This is a cool piece if you main something like tiphia sting, switch to this for vokes, casting, etc, 1% enmity is better than nothing, its not like any other stats will help your provoke.
The plus one this is the only piece that really makes a difference for pld. next best would probably be Rosenbogen +1 for the extra hp and vit. The MDB Maletaru was mentioning isn't worth much since the NQ is less than 1% damage reduction and the HQ is both expensive and still only offering a marginal decrease in magic damage less than 2%.
Enmity helps the most if the rest of the gear is spec'ed for def and damage reduction. If you are good on enmity then the next best would probably be Rosenbogen.
@Anza
This is also a great piece for RDM/NIN as well. It isn't "PLD macro piece only." In fact this is a great piece for kiting to macro in when you're casting spells and/or job abilities to get enmity. Just as long as you don't idle and know it's macro only. ^^