Well, let's take a look at it. It's useable only 1/day, which right off the bat reduces not only it's book value, but also it's in game value. Now, if you want to use the ring, this is what will happen on your turn. You take a move (move action), activate the ring (standard action), and do nothing else, waiting until the next round to make your +20 attack, as your round is now over. But what if you're hasted? Ok. No problem. You take a move (move action), activate the ring (standard action), take one attack (haste action). Or, if you're hasted you can also do this: You activate your ring (haste action), take a 5-foot step, take a full-attack action, in which case you get +20 on your first attack roll. So, unless you are hasted, using the ring is costly, as you must give up a healthy portion of your round to activate it. If you are in fact hasted, then using the ring is a little easier, but there will be times when you might rather use your haste action for something else, say, an extra attack at your highest bonus for example.