Does the ES sport a rebaged Rokkor? The Konica Auto S3, Minolta 7sii, Vivitar ES and ???? escaping me right now, are all built more or less on the same body and were made by Cosina. Obvously the S3 has a Konica 38/1.8 lens while the others all have a 40/1.7 (potentially all the Rokkor). Though all built in the same shell, they do have slight differences. Most notably in the S3 which has no manual mode and an advanced funky flash system. The others differ more or less only cosmetically.
I owned an S3, it is a tiny well made camera. I was not overwhelmed by the lens, though it was good. I had a very good Canonet GIII and Minolta Hi Matic 9 (the best of the lenses in these cameras that I had) with great lenses, the Konica just was different and not as much to my taste. But it fit in a pocket and was very quick to use.
I am looking for a 7sii, by the way, very nice cameras.