It destroys small engines..My Stihl dealer insists that his customers use Premium fuel, that has NO ethanol,
Yep - and unfortunately I have to drive nearly an hour to reach the nearest ethanol-free fuel location. Of course, there's always the "canned" small engine fuels that go for around $20 per gallon.
There's a federal standard for off-road and small engine fuel, currently called REC90. It's nearly impossible to find, though - even at marina fuel docks.