Was browsing a seller's listings on eBay and stumbled upon a Simplex SX2 derailleur. I'd never heard of it before. I saw an entry in Velobase with no years attached. I saw nothing in Disraeli Gears. This sure looks like Simplex went all in on Delrin at this point. The parallelogram seems to be stamped steel, but everything else is plastic. Targeted for the kid's bike market? The fasteners make it look like the target was Wal-Mart bikes.

https://www.ebay.com/itm/301713636387