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 159+4294966701+1668+7281) -- 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 did not realize this when I changed my rails several years and app. 40-50k miles ago. So, I used the plastic rails. Of course, had I known then that there were metal rails, I would have used them instead -- considering how crucial they are to the engine's timing, and the plastic 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.
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