Universal plates support both ANSI and ISO layouts. ANSI layout is the standard layout used in the United States and many other countries while ISO layout is the standard layout used in many European countries.
ANSI Half is a plate with one large cutout for the alpha cluster. This allows switches in the alpha positions to take advantage of the flex cuts in the PCB. If you select the Half plate option, you must pair it with a soldered PCB.
For plate materials, bottom-out firmness and acoustics are considerations of preference. In our experience, softer materials may help reduce finger fatigue for long typing sessions, while firmer materials may provide a more responsive feel. The order of plate materials from soft to firm is POM, Polycarbonate, FR4, CF, Aluminum, Copper, and Brass.