Disagree, one on one means that the striker should score when clean through on goal (doesn't always happen though). Penalty specialist has the cool, calm temperament to score from a penalty. I have found that using FK takers to take penalties means that it normally goes over the bar.
I don't have a specialist penalty taker in my squad, so use my main FK taker. He has a 66.6...% success rate (4 scores, 2 saved by keeper).
Any formation or tactics advice given is based purely on experience with my teams...