I'm planning on buying a pair of cheap SPD-SL pedals to replace the worn-out PD-R540 that my father gave me. These two are on the lowest-end of Shimano's range.

PD-R550
PD-RS500

The R550 is Tiagra-grade and seems to be of an older design whereas the RS500 is non-series but is seemingly based on the current generation of higher-end pedals (looks very similar to the PD-R7000 in fact). The R550 has a larger metal wear plate but the newer, higher-end pedals from Shimano seem to have ditched that so I guess it's not really more durable? I don't even think I can get replacement ones where I'm from if they ever wear out. The R550 costs 15 USD more than the RS500 here in my country and I have to order it online since my LBS only has the RS500 in stock. What do you think, should I just go with the cheaper one? Is there even any noticeable difference between the two?