It produces 1.7 litres of water per day.
The round shape is probably easier and cheaper to produce.
And older article on the Watercone (when the inventor first came up with it and was looking for financial backers) said the price was $150 US per unit. That's pretty expensive, even if it was made from Lexan.
http://www.halfbakery.com/idea/Ultra-Cheap_20Solar_20Water_20DistillationEdit: That was the price in 2006, the price indicated on the site is $50 US. Still high for the people who really need it.
Sue