The Iris is my favorite keyboard. I have built 3 of them so far. I agree about the top thumb cluster switches, but I put encoders on mine. I still don’t use them much, but they are “neat”. The bottom outside thumb cluster are extremely comfortable for my hands (it’s where my thumbs naturally rest) and are some of my most used keys (enter and fn). Space is my middle thumb cluster which is also great. The inner most ones are the hardest to reach, but are reserved for alt and win.