I've used them. Right before I left the weld shop I was working at they asked for suggestions on things to buy and I suggested a few Piher clamps. Don't recall the models we got, but they were pretty standard size clamps for general fab work, 16" or 18" overall length. That was a very expensive life decision for me. They are incredible! The model we got had groves to help grab pipe or tube, there was extremely little flex when locking down on a part so it didn't push things sideways on you, and holy clamping force batman!! The biggest downside to them aside from expense is weight. They are bulky and heavy. I wouldn't go replace all my standard F clamps with them just because of the weight, but I would definitely recommend grabbing a pair to try out.