I don't know if there are any tutorials, but they can be used on fondant or a good crusted bc..........I did mine on bc. I sprinkled a tiny bit of powdered sugar on the mat, then dusted the excess off to keep from sticking to the icing, and gently pressed it into the cake, make a handle on the back of the mat with scotch tape or something, so you can pick it up off the cake, then wipe the grease off between each time, so it doesn't get sticky.
I use this tool to make a diamond pattern on cakes. It works on buttercream, whipped cream, and fondant. I have never used the diamond impression mat, but that sounds cool, too! 
I just did a wedding cake with the quilting and i purchased a square cut out set, it has 3 different sizes of individual metal square cutters, it didn't take long to imprint each diamond individually, i used the middle sized square
Quote by @%username% on %date%
%body%