My MP40's (older white box) work just fine on my 3/4" acrylic, but it would be iffy on 1", if it works at all. They do slide a bit on 3/4" and require mounting the cord properly at that thickness.
The MP60 works fine at 3/4" with spacer, so I think no spacer (it already has a built in rubber pad of sorts) it should do fine as advertised on 1". Would be interesting to see how people recommend mounting the MP60 (by the cord?) at 1", or if there is a special thin spacer that allows you to support spacer rather than the unit directly.