For the why bronze question, it is a matter of cost. It is strong enough for this application and significantly cheaper than a machined part. I had my drivers side trip machined out of 4140 and I can have the molds built and ~10 trips cast for what that cost. The mold tree does 20 trips (10 of each trip) so it is quite a bit more expensive than the 1 that I need for my passenger side, but this is a part that is a known-bad design that fails. I figured that there were a lot of others out there that had a broken trip and might need one to get their door handle working again. If there is enough interest that I don't loose money, I will have a batch run. If not, I will just machine my passenger trip out of 4140.
Final price will depend on interest, but they will likely be between $50 and $75 each.