Actually Aggeman, I'm with you (after I had the night to think it over). There is a rule hidden in with bucklers that basically state that if you use the arm the shield is on for something, then you can't get the armor bonus for the shield that round. That's an offical rule.
The fluff text in the item basically states that since you can dispell/resummon the shield as a free action then you don't suffer an arcane spell failure chance or armor penalty. This doesn't mean, in my opinion, that it affects how the shield works. A mage with this ring could, drop the shield on his left hand, cast a spell with his right (thus no penalty), and then resummon the shield on his left to retain his +2 AC. If, however, he cast the spell with the same hand as the shield is on, then no, he wouldn't get the AC bonus after the spell is cast.
This is in keeping with an established rule within 3E, and with the fluff text (as many casters would be using the non-shield hand to cast).
Yes, the item might be a little overpriced for it's power, but it's still useful. A 2H fighter could hold his weapon in one hand while the shield is up and thus gain the +2 AC bonus for any AoO he might incur before he makes his attack, and then dispell the shield before attacking with two hands.
A wizard could use this item on his left hand and cast spells with his right all day without any chance of spell failure.
A cleric in melee could drop the shield and cast a cure spell on a fallen comrade without going through the trouble of putting away or dropping his weapon first. Sure, he doesn't get his +2 on AC for the rest of the round, but at least he's not weaponless.
A fighter in a town with laws against armor will always have a shield ready.
Anyway, the point is, I have to go with exisiting rules when I can and this is one place where there is an existing rule and despite my earlier belief that this item broke that inconsistency I know think that the fluff text was just not fleshed out enough.
The price of the item is a little high, but I don't think it justifies breaking an exisiting rule.
IceBear