Metal vs Plastic Chain Rail Question

As I was just looking at the upper timing chain rails for the 380sl on several websites, -- e.g.,

and --I happened to notice that there are plastic rails made by Swag for$4-5@ and metal rails made by Meyle for close to $20@. However, I didnot realize this when I changed my rails several years and app. 40-50kmiles ago. So, I used the plastic rails. Of course, had I known thenthat there were metal rails, I would have used them instead --considering how crucial they are to the engine's timing, and theplastic ones' tendency to crack with age. I was therefore wondering if the metal rails are new, and if other people have also replaced their rails with the plastic ones -- either because people didn't realize that metal ones existed, or because the metal ones don't have a big advantage for some reasons.

Thanks very much for the info.

Bill