Cook's Illustrated covered potato nails in the July/August 2014 issue, page 3.
They took three potatoes of the same weight and baked them in the same 350*F oven. One plain, one with an aluminum potato nail, and one on a stainless steel skewer. Potatoes were rotated after 30 minutes. Total baking times are not listed in the article, but the potato nail version finished first, the stainless steel skewer was second, and the plain potato was third. But there was only a 7 minute difference between potato nail and plain.
They also ran five potato nails through a single potato and it cooked 11 minutes faster than a plain potato.
Their conclusion: "Potato nails aren't really worth the investment." If you want faster baked potatoes, Cook's recommends poking a potato with a fork several times and microwaving until slightly soft, 6-12 minutes, flipping half way through that micro time. Finish in a 450*F oven on the middle rack, about 20 minutes until a skewer goes in easily.
They took three potatoes of the same weight and baked them in the same 350*F oven. One plain, one with an aluminum potato nail, and one on a stainless steel skewer. Potatoes were rotated after 30 minutes. Total baking times are not listed in the article, but the potato nail version finished first, the stainless steel skewer was second, and the plain potato was third. But there was only a 7 minute difference between potato nail and plain.
They also ran five potato nails through a single potato and it cooked 11 minutes faster than a plain potato.
Their conclusion: "Potato nails aren't really worth the investment." If you want faster baked potatoes, Cook's recommends poking a potato with a fork several times and microwaving until slightly soft, 6-12 minutes, flipping half way through that micro time. Finish in a 450*F oven on the middle rack, about 20 minutes until a skewer goes in easily.
