Tiger Woods would not use one if he wasn't getting paid, simple as that. Mickelson was right when he said they are inferior. It is impressive however, that Nike keeps getting people to buy them, but again, that's why they have Tiger. It's all marketing.
My problem with them is simply that - they are inferior. They don't have to build good products because as long as people see Tiger playing them, they will buy them by the truck loads, even if they can hit something 20 times better. They convince themselves that a Nike is the best club for them, because they want what they think Tiger has.