been about a week since using oatmeal for my microwrms. I will say, IME, that oatmeal is so much better than potatoes it is almost ridiculous. worms appear in a thick layer on the surface, moisture level is much easier to manage, worms are covering the lowest 1/4-1/2" of the container sides above the medium, and for a few inches past that there are still plenty of worms on the container sides to collect.
20L My Other Tank: OEBT Shrimp
40B Inlaws Tank: 2 goldfish
75 Main Tank w/ sump: 5 Glossolepis pseudoincisus, 5 Melanotaenia boesemani, 10 Melanotaenia praecox, 5 Melanotaenia lacustris, some cories, a bn pleco and rainbow fish fry