I have one of these and I love it. I don't think the bag is supposed to last until the container gets filled. For those of you that have every used a diaper genie its the same concept. It definitely cuts down odor and stores it if your regular garbage isn't full. You when you cut the bag to throw out a full container your hands never have to touch anything icky. The inside of it stays completely clean and your hands never touch anything to throw it out.
On the downside I do agree with a larger unit for multiple cats, the refills are expensive and it may be confusing to use it in the beginning.