However, eggcrate is 3/8" square as opposed to 1/4" netting. We can't make a blanket condemnation of eggcrate as its relative to the size of the smallest fish. And there aren't many fish that we keep that would fit through 3/8"...
Another excellent alternative to keep fish out of the overflow is plastic gutter guard commonly found at Ace Hardware.
Almost ALL fairy and flasher wrasses, dartfish, dottybacks, blennies, gobies, etc will 'shoot' right thru eggcrate...even those that appear bigger than 3/8"
I agree with the use of gutter guard, and have often posted pics of my overflows that are 'sealed' with it... Not a single fish into overflow in over 5 years...