The outside surface facing the chain is a hard rubber. I think that they are great insurance because they aren't going to break (if they break, you have problems a lot worse than a timing chain). Too bad they aren't made (
AFAIK) for an aluminum M117.
Unless the pins are damaged when removed, I think they can be reused. I run a tap through them before pulling - and make really certain that the tool stud is in all they way - that way, damage is very unlikely.