Did I miss something in your example, Richard?

For the first 3 years, at $33/month vs $8.80 per month the SWF costs roughly 2 1/2 times what the bleach does. That means the 3 year cost of the SWG buys 8 years worth of chlorine. After that, the cost for the SWG is about 10% higher than the chlorine. So after 3 years you are 5 years behind the cost of the chlorine...and you will never catch up. But how much is the convenience worth to you? If the convenience is worth it, then it's worth it. If it's not then it's a bad deal.

Now suppose you are a super-high priced lawyer or doctor making $300/hour--If you spend an hour every month going and getting chlorine, your time cost outweighs the chlorine cost so the SWG saves more. Of course, you COULD hire someone to get you chlorine once a month--and it would not be $300 for the labor.

I suppose I could keep coming up with scenarios all night!