Also on an Iris (this very second) having moved from a Let's Split. I'm a HUGE proponent of hold/tap for modifiers and programming brackets. All the ones I use most are under my thumbs with that change. I actually have symmetric modifiers on the thumbs because I effectively have double the keys. Also all my layer changes are from holding down F, D, or S which turns the right half into (respectively) arrows, numpad, and symbol pad.