I'm not picking on this company and I don't know if this is true of their u-joint conversion because I don't know anything about them. I do know that most of the driveshaft shops that put in a greasable, replacable joint, use an early Ford Falcon joint that was not designed for the application.

There is a driveshaft company in Arizona named Bejer (not sure of the spelling) that does a beautiful job with these shafts and use a stronger joint.

Good luck,