Generally you don't want to try cutting this stuff. Most the official documents state that these blocks cannot be cut. This means that layout is critical before starting the project. There are some options as the blocks come in 12x12,8x8, 4x8 and 6x8 squares.
I haven't set my shower wall yet, but plan to build a "story pole" with marks every 8" on the wall so I can make sure that the wall is setting up and there is no "creep" as I go. I will have to allow for the tile/thinset thickness of the shower curb, and may need to do some drywall adjustments at the top of my shower before starting so that their are no gaps at the top.
I have a wet saw, so in theory I could try cutting one, but it might be a rather dangerous operation. I've cut glass tile (1/8 thick approx) with the wet saw no problem, that was for a marble shower with blue glass accents... this is a 4" thick piece, so might not be a nice scene if it were to crack and send jagged slivers out and about (face arms legs etc)... so I wouldn't want to try cutting these myself.
You might find someone at a glass shop willing to play with them.