What I'm saying is that the only real use for the ring is for people using a two handed weapon. Allowing you to get a two-handed attack and still receive a +2 AC bonus seems to be exactly what it's intended for.
The only other situation where it would be useful is in the case of a caster who wears armor and uses a weapon and shield (spellsword, for example). It would allow them to free up their hand to cast a spell.
At the level most characters can get it, it's less effective than a magical shield that costs less. For most shield fighters, it's simply not worth the cost.
It's almost never useful to a pure arcane caster, since it will not stack with bracers or mage armor.
It's marginally useful for a cleric, but most of those who use shields would prefer a magical shield with a higher armor bonus.
If you don't allow two-handed fighters to use it, it's just an overpriced bauble with very little practical use.
Paying 8,500 gp for +2 AC that you end up only using against incorporeal creatures (and not even then if you are an arcane caster) isn't worth the price for most PC's.