The ES models are from the time period around 1998 - 2004. The Festool name was first used in 2000, before that the brand was called Festo. In 2004/2005 the first ETS models appeared.
If you have the tool at hand, the production date is on the sticker.
The upgrade to the ETS models mainly involved a slightly heavier counterweight and fan so that it vibrated less, which is good for your hands. The plastic outher shell was also updated. But the motor, bearings and electronics remained the same. In practice, you will not notice any real difference.
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