Product review (5 stars): It actually works!!
All my glass items -- wine glasses, water glasses, pyrex cooking dishes -- were coming out of my dishwater cloudy and water-spotted.  I thought this was being caused by the detergent I was using, but that turned out not to be the case.  After a little research online, I came to the conclusion that the problem was the mineral-rich "hard" water in my city.

I looked at the in-line filters that can be installed in the water line.  They're probably the best solution overall, but they're expensive, and the replacement filters are expensive too.

These filters are a better value, I think.  The cloudiness and water spotting have all but disappeared since I've put one in my machine.  Its possible that an in-line filter would do a slightly better job, I suppose.  But I am very satisfied with the results of these filters.