if your talking current flights then the main diffs are strength, weight and cost
flights are double pinch, ie 2 bolts clamp the arms to the spindles, they are heat treated 2mm thick cromo, strong but light.
proline are single pinch, ie 1 bolt, cromo tubular which has a bigger cross section to achieve the strength and therefore heavier. they are cheaper to manufacture hence diff in price. still good cranks though. I have a set on my race bike and they are pretty good.
I think the splines on the spindles are different and diff materials too.
cheers Marc
