It's definitely a combo of different materials......the linkage arm , hook and turnbuckle are some sort of tough Nylon composite it seems......Hook arm is the same thing cable guards are made from (carbon).
The shelf is aluminum ( I assume).
I'm guessing that the actual hook itself would bend before breaking, and simply return to it's normal position. It's not brittle.

I'm pretty sure I could break it.....if I tried, but I don't see any "Normal" use causing any problems.It may actually prove to be MORE durable than many rests.....at least that's the way it's heading for me.

Mines been up and down a few trees this year, and had 1000's of shots wrung through it and it's still right where I put it.