In my hands what makes David's chisels special is that they are harder than all but Japanese chisels and they have a handle that is the most comfortable of any chisel handle I have used.  We probably will never see a commercial chisel heat treated to this high hardness and in this style.  Careless owners would break them doing things with a paring chisel that a paring chisel is not designed for.  

Chisel handles don't get much mention when chisels are discussed.  But it is the handle that connects the chisel to the user.  While the eye may note the details Wiley enumerated it will be the hand that discovers the best feature of these chisels.   Commercial chisels could easily be made with handles like these.