Not trying to start any arguments here but as a part time taxidermist (hobby) I was trained by the local taxidermist here. He has mounted animals both ways, I have seen mounts of his that were chemically tanned that are over 20 years old and still look great. As far as shinking, a chemically tanned hide will shrink, but only where it has room. I can only imagine the hide that could shrink enough to deform the manikin it is mounted on. In my humble opinion, as long as the hide to be chemically tanned is properly fleshed,sewn etc. you should have a quality mount for years to come. The key is quality, I have seen plenty of really Shxtty mounts out there. Find a taxidermist you are comfortable with, look at some of his/her work and ask questions!

Good luck!