Well Jay, I see that you have heard of John Neeman too! I've bought a few of their tools, and have been very happy so far. They do some very nice work and I've been thinking about having them make drift pins all well. They are my go to tool people!

But back to the relevant topic. You mentioned that you use metal hammers for striking your chisels as well as your pegs. I use a small metal sledge for driving pegs. I find that wooden mallets are harder on the peg (more strikes to drive= more chance of damaging the peg). It is also pretty hard on the wooden mallet.

I use a wooden mallet for striking chisels though, in the style used by Chappell. I can see the appeal of using a metal hammer with chisels. Greater weight in a smaller size leading to a more controllable amount of force applied with a minimum of strokes.
How do you avoid premature damage to the chisel handle? Avoiding damage to the handle has always been the rationale for the wooden mallets in what I have seen. I would guess that one would want a relatively soft steel for such a job? Maybe even bronze?
Perhaps avoiding chisel handle damage has more to do with striking technique and attention to detail when making one's chisel handles than choice of striking tool?
I have never really tested out the concept of the metal hammer for chisel work myself, I think I will though. To be quite honest, I was always under the impression that to strike a timber framing chisel with a metal hammer would be such an act of sacrilegious barbarity that the Timber Frame Gods would immediately cast me into a pit of seething condo framers with nail guns! I suppose I'll have to rethink that assumption...