Thank everyone for the thoughtful responses.
The reason I wanted to try purigen is the fact that I've seen examples of established, clean, and maintained natural tanks, and then examples of tanks that use purigen and there is still
a big difference in the way it looks. It seems that no matter how well maintained the tank may be, there is still that ever-so-slight murky white tinge, especially visible right under the light.
Here is a video of a small tank in which the owner claims to use purigen. http://www.youtube.com/watch?v=UIoPZ...175b21c8bc.jpg
The tank isn't planted, but it's still stunning. It's definitely in the "less is more" category. Please tell me if I'm missing something obvious here. The guy says all he does to keep it clear is normal maintenance and use purigen, but I suppose he could be dumping in water clarifiers by the bottle for all I know. Not even the likely chemical-laden tanks at the LFS are that clear.
Here is a video of an obviously well-maintained tank without the use of purigen exhibiting the slight cloudiness.
I suppose it's a matter of priority. Do you want to have a more or less self sustained ecosystem in a box with little to no maintenance outside of water changes, feedings, and an occasional filter cleaning (if a filter is used at all), or do you want your tank to look extraordinarily clean and clear while potentially slowing the growth of your plants and adding a little to your running cost? Lets face it, nowhere in nature is a body of water ever "crystal clear", so that attribute itself could be seen as unnatural. Nonetheless it's impressive and highly sought after in the aquarium hobby.
So I think you're absolutely correct in saying there is no need for products like this, and in most cases (when properly maintained) tanks are plenty clear enough to satisfy their owner's expectations. However, after seeing what is possible, I can't help but want to try it for myself.