Not the fluffiest muffins, but certainly not hockey pucks like some reviews make them seem. I subbed buttermilk and also added a cup of sugared blueberries. Very good!
Worked great as-is! They tasted plenty peanut-buttery to me. The 10 minute time also worked fine for me. Crispy on the outside, chewy on the inside. If you're looking for in-your-face peanut butter flavor, go ahead and make the adjustments suggested by others, but for me, it's great.