It's a nice item. It's very handy when you want to travel, although the one week activation period can be a little annoying. The extra time in the day is nice, but only nice.
But the powers of the ring attemtps to answer questions that sometimes are best left unanswered. Do you eat to live, or do you live to eat? The ring suggests the former, but eating is more than just sustaining yourself. In most human societies, eating forms the basic bonding ritual of any large group. The Europeans, bringing back spices from the crusades threw away the dark ages and brought in the age of spicy rennisance. Wine, it is said, gladens the heart of the drinker. Food and drink are more than mere sustinance. The ring forgets that.
Likewise unless you are in a tower working on your magic item, those extra hours are going to be wasted. Sure you can do extra guard duty, and you can spend less time in a vunlerable state, but in the long run, extra hours does not mean extra work. There are more factors than mere desire for sleep that forces a mind to seek recreation. After all, you're not sleeping now right? This time could better spent working, so why aren't you working?
Thus there are situations where this ring would be exceptionally usefull, but not always. Besides the notion that you can not eat anything and still not loose a single pound of weight would drive me batty in a month.
If you are just thinking of the food aspects alone, you can get a Sustaining Spoon for over twice the price (5,400 gp) and feed youself and three others. This can be important because even with two hours of sleep it is still unwise to travel
alone and it your companions have to eat, you still have all the problems even if they only indirectly impact you. Moreover, the spoon can sustain you, a companion, your mount, and your companion's mount, something the ring alone cannot do.
Not eating alone, or eating cream of wheat with a friend. Neither sounds all that appealing to me personally.