the perfect condition for an egg is to be in 100% humidity without getting wet.
some breeders who use substrate continues to use it. if it works, why change it.
I use a light diffuser, water, and press n seal with my 6 or 12 quart tub with lid depending on the clutch size. I use to use perlite in the water so when I check on the eggs, they didn't get splash with a little water. I now just use distilled water. I also use plastic spoons and I break off the handle and use them as stops so my loose eggs don't roll. I stick the handles into the diffuser.
the big advantage with the light grid is the eggs are not in anything thats close to being wet. less chance for errors, more so with someone new at it.
I place the press n seal on the tub and then place the lid over that. helps keeping the press n seal from lifting.
I check my eggs weekly which lets fresh air in. the last 10 to 14 days, I remove the lid and peel a corner of the press n seal back to make a very small air hole.
this works well in keeping the eggs from caving in, very easy, no guesting if the media is too wet too dry or needs water added later.