I am a Glazier by trade and I do lots of re-screening of large screen windows and doors. I have made a similar clamp add-on using an old car scissor jack handle to turn the clamp handle to hold the frames in place mounted right onto my work table using two sets of screw in hooks facing each other to hold the handle in place.
Good idea. Wish I thought of that or saw this when I was clamping up a cabinet.
Fat hands, little clearance, no leverage = sloppy clamp job.
The picture is not indicative of its use. If the clamp handle was up against a flat surface that did not allow for your hand to wrap around it; the allen key would be a means of torqueing it tight. I'd merely use a different type of clamp like a wood screw.
Adding hardware is often one of the trickier parts of a project, and this toolbox is no exception. In this video, Matt installs the door pins and lock in a way that ensures perfect alignment of the door.