Review on EPAuto Cr-V Universal Joint Set with 3 Pieces for Impact Applications by Andrew Griggs

I'd say I used them quite a bit for "heavy duty work" (loosening and tightening heavy bolts on several cars that had NO rust). They worked very well and didn't show even the slightest sign of failure or starting to work. I haven't used them for anything crazy like loosening a rusty bolt while leaning on a large breaking bar or similar, so I can't rule out the durability issues some others have experienced.