there's probably as many answeres as there are irons- i've heard of salt- brown paper bags- dryer sheets- there are a dozen or so iron cleaner products in the grocery store (laundry isle)
my iron does NOT have a non-stick coating on it- i've crumpled up aluminum foil and used it on the hot plate to remove fusable- with great success- i'd be afraid of damaging a coating if there was one though.
once you get it clean again- start using a pressing sheet when working with fusables= will really save your iron and other surfaces-
there are plenty of options for pressing sheets- you can purchase one from a quilt/fabric shop (quite pricy)
you can use the release paper from fusable- after the fusable is used- and you peel the paper away- the paper works well to put over your appliques before pressing=
or you can use parchment paper- available in the grocery store- right next to the freezer paper (these two items are main stays in my sewing room- the room would be 'naked' without them :) )
i agree with your m-i-l---crazy
my $10 iron is a wonderful iron that has held up way longer than that stupid iron i paid $149 for- that was leaking-sputtering- horrible in less than 3 months