Do the bent anchor shafts mentioned in Practical Sailor bother you? How about the steel quality the bolts are made of ? I have one and so no reason tp find the claims its better than its predacessors Rocna or Manson.
Chef2sail, Practical Sailor has never reported a bent Mantus Shank, as you state in your post.
However, shanks of any design can bend and where we stand with our shanks is clearly explained in this write up.... Anchor Shank Strength for Lateral Applied Loads
We also have a life time warranty on our anchors and ship replacement parts at our expense.
As far as the bolts go,
Even though we currently use Grade 5 bolts the anchor was designed and sized for use with Grade 2 bolts.
For example a Mantus 35-lbs anchor has FOUR 1/2-in bolts at the shank joint. Each 1/2-in Grade 5 (120 ksi) bolt has ultimate tensile strength (UTS) of 24,000-lbs. Compare that to the 5/16-in High Tensile (HT) chain which has UTS = 11,700-lbs.
Each bolt is twice as strong as the chain & there are four bolts, so the Mantus joint is 8x as strong as the chain.
Simple math gives you - Mantus shank joint UTS = 96,000 lbs
5/16" HT chain - UTS = 11,700 lbs.
For Grade 2 (74 ksi) bolts the UTS =14,800-lbs. A single 1/2" Grade 2 bolt is still stronger than the HT chain. And the Mantus shank joint with four Grade 2 bolts has UTS = 59,200-lbs and is 5x as strong as the 5/16" HT chain.
reference bolt strength data
Happy Mardi Gras!