I've found that taking the same reading twice on the same scale is liable to produce a second reading error if the first one is read wrong. I originally thought I would hook two tapes to the nails, and read them one after the other, but found the one I used. It was the first time I'd used the feet/inches scale - I much prefer decimal feet.
I also have to take more care when reading a metric tape. I've found that even people who live in metric-using countries sometimes have a hard time getting the decimal point in the right place.
What I like about using feet is that the whole foot is right in front of my eyes, and I easily see the fractional foot.
But I do use meters in all my race calculations except for mile splits.