Technically not mine but there is one sitting in my fathers shop here in Kitchener. Well technically, theirs two, along with a wire bender 
Edit, and to shed a little light on the subject in regards to kinking. That can partial be with thin wall material only and the thicker it gets you can at times get away without even using the mandrel and still get a perfect bend. But the kinking isn’t the only issue, when you bend the tubing you deform the round shape to a slight egg shape and when it comes to Roll Cages some inspectors will measure that deformity to see if its within tolerance. But the deformity is always greater on a manual, none mandrel bender because their is no mandrel on the inside following the bend as she goes…