High performance axle shafts are a little softer than stock axleshafts.
This allows shock loading (drag race starts) without breakage.
Because they are softer, they tend to to twist a little easier.
It is easy to inspect and see how much twist there is. Just pull the shaft and look at the splines.
The best way to check for twist is to paint a straight line down the length of the shaft on the first time installation. The amount of twist will be surprising. Up to 1 full revolution.
You have to contact the manufacturer to find out when how much twist is allowable before replacement is required.