1.Tightened gripping u-bolts apply crushing stresses to the pipe wall. not good if high pressure.
2.U-bolts have a tendancy to dig in with large
displacements
3.U-bolts can loosen when subjected to cyclic movements.
4.Mr fitter usually fits the wrong bolt the wrong way.

U-bolts are fine if used for their proper purpose, ie not stress critical piping.
Play safe and if the support is critical, make it a proper shoe. a no risk option!