I've found the small keys on the thumb clusters on the Ergodox to be a good location for select function keys. I don't have to hit them often, but much of the time I do, it must be in combination with some modifier keys for certain IDE shortcuts. I have seen layouts online where people assign nothing to them. As for the big keys on the thumb clusters, I don't find them to be an issue. I do think it would be better if they were moved in just a hair though.