What do I do with the edges / corners?

The Premium version is very stiff, so it can not be folded around corners or "kinked".
Therefore, at the corners you must cut the material apart with a sharp cutter or scissors. Then the kitchen splashback parts are applied on butt.

If desired, you can use silicone to seal the seam. The same applies to the end pieces on the sides.

Alternatively, you buy a corner profile in the hardware store, cut it to length and stick it as corner protection and visual embellishment onto the corners.

You can acquire corner profiles made of aluminum or PVC and in different colors for instance at Bauhaus.