I have used them, running them through the Cuttlebug and the GC...  they emboss really well.  Though the tab attached only gives you the option of embossing at the edge of your paper/card.  I was making a wedding card and used one of the fancy swirls , that Joanna sells at a brilliant price, in a bottom corner of an A5 vellum, it looked lovely.

We also have the larger masks (sadly out of stock), which embossed on 160gsm card lovely.

As I said the only problem I had was with the tabs, wish the weren't there, but that is a personal quirk of mine, I like to place masks where I like smiley: wink

hugs Janie xxx