Exactly how much horsepower (actually number and percentage - and please make sure the guy writing the article wasn't trying to sell you something) was lost (fans don't increase HP, they require HP to operate) due to the flex fan vs the clutch fan? And what type of flex fan was used?
The fact is that for street cars, cooling (which is more important than a little extra HP) is typically enhanced by an appropriately sized and designed flex fan. Flex fans have been around longer than you and I have and don't seem to be loosing popularity, except in the cases where every last ounce of HP is required or some one has fallen for the hype of free HP. In that case, one or more electric fans are in order - and those aren't a totally free ride either. Sorry, just Physics.
In fact, the engine tested made more horsepower with the clutch fan than it did with no fan at all.
That statement alone raises doubts to the validity of the "test".