Yes, Omega did make quite a few watches that weren't part of a series like Constellation or Seamaster. The front crystal would be plastic / acrylic (called Hesalite). If the dial is original I'd say it's a good purchase up to $375 but count on having it serviced. 85% of the watches I've bought off eBay need a cleaning, oiling and adjusting (the basic service done to a watch) whether or not the seller said it was serviced.
And the crown is a replacement as Kyle pointed out.
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