(:1f539:) How fragile are marble waterjet mosaic tiles?
As with anything, they need to be treated and handled carefully. That being said, they do require a sense of delicacy when cutting and installing.
(:1f539:) What thinset should be used when installing a marble waterjet tile?
Always use a WHITE, latex modified thinset when installing a marble waterjet mosaic tile. The latex additive helps with offering some flex for the marble tiles.
(:1f539:) Will certain types of grout scratch the polish in a waterjet marble tile?
The biggest concern will be a sanded grout. These contain sand particles that will scratch the grout. IF you are thinking of a darker color grout, you want to seal the marble first before installing the grout so it will not stain the marble.
(:1f539:) Are marble waterjet mosaic tiles ok for a shower?