> a user needs to easily differentiate between 1, I, |, and l along with 0 and O.
Most of the times, a font present those characters side by side, to show their differences and to illustrate the fact that they can be easily differentiated.
But what we need is not differentiate between them, but identify precisely every single one of them when presented without the other as a comparison point.
Almost every font presented in the article makes that mistake: for example, 0 is almost always the exact same shape and size compared to O, except for a dot or a slash across the 0. This allows you to recognize a 0 at first glance, but not a O. The same issue is also present in a lot of the presented fonts with l that can be mistaken for a 1.