I guess you could use one per day--switching them out at the end of each night--and waltz around town telling all the gawkers, "Oh, this? This is the Final Fantasy keychain I use on the sixth of every month. Wait until you see tomorrow's!"
Or you could do what most people who wind up buying a set will do in the end--which is keep them boxed up in the back of your closet. (No hate--I'd do the same!)
Should you want to buy them anyway, head on over to shopncsx.com sometime between now and late September and plop down a pre-order.