A B/P u-joint is not a flexible shaft, but sometimes it can act like one. A single B/P joint can handle up to 35 degrees of misalignment between two shafts. Two joints linked together in series can accommodate 70 degrees of misalignment. The typical cross-type joint can only manage about 20 degrees of misalignment.
So, when the misalignment is deep into double digits, think B/P joints first.