Has anyone used bridge pins of different materials and, if so, what are your opinions?
This reminds me of the hype about "monster" speaker cables. That is, if you use giant wires, like from an arc welder, your speakers will sound better. What about that tiny wire that goes to and from the transistors? Companies have been built on this myth, and more than a few bucks spent on ivory pins. I can't speak to guitar pins, but I can speak to superstition, suggestibility and gullability.
I use bone - a nice compromise between looks, cost and functionality. Besides, it's green. Making plastic is a nasty business.
Be well, practice a lot and enjoy your guitar.