If I remember right, the higher upper ball joint mount allows the spindle to be used on a 4WD and 2WD truck and keeps the axle boot away from the upper ball joint at all angles. The McGaughys may require more of the ball joint shaft to be cut off below the ball joint nut. I've never ran McGaughys spindles, so maybe somebody with a 4WD could chime in. I have ran Belltech spindles on about 6 vehicles and with no issues at all with bumpsteer on everything from street driven trucks and cars to full on drag cars. It's when you combine the spindle with springs or struts for a lower drop that you can possibly run into bumpsteer headaches.
Just as information, the grade 9 hardware exceeds the factory bolt specs, which I "think" is grade 5, and the two grade 9 bolts holding the strut mount will exceed 1 ball joint nut holding the spindle. Mine has been flawless and I'm sure the company has many other trucks using the same set up. As I mentioned before, if it wasn't "safe" a company like Rough Country wouldn't put their business on the line for it. Can it be broken... sure if you abuse it. Some people including myself can break an anvil. It takes sense enough to know that you've lowered the truck and what the new limitations will be.