From the Festool FAQ database (see top left corner of www.festoolusa.com):
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We recommend the ETS 150/3 for polishing seams on granite composite countertops using 180, 320, 500 and 800 Titan 2 abrasives. Any of the Festool random orbital sanders can be for this application, some prefer ETS 150/5 as it has a more aggressive sanding stroke. Either sander provides one-handed ease of use, and the best dust extraction in the industry.
When fabricating granite composite countertops, you glue the apron to the deck, round over the edge, then sand the glue seem from 180-800 grit to bring the edge as close as possible to the factory finish. Do not attempt to sand or polish the surface of granite composite as you may scratch and dull the surface. Always follow the manufacturer?s recommendations for cleaning and care.
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Hope that answers your question.
Christian
Festool USA