Shoot N C targets really helped me improve my aim. The problem is the Indoor range I typically go to has crappy lighting and I wear glasses. If it is hot at all I tend to sweat and sooner or later the glasses get a little splotchy. Add in the fact that the indoor lighting is bad and on a good day its not too easy to see the holes in the target 30 feet away you have a problem.
With the Shoot N C Targets it is so damn easy to see where you are hitting and adjust your aim its not even funny. Not only is it fun to see the holes I really see the value in paying a little extra money for them. If you get the smaller ones(about the size of a pie plate) they are actaully pretty fairly priced.