Why the grid, and not a checklist
A checklist shows you today. Today is where you log, and it is the worst place to judge whether a habit is holding, because a single day tells you nothing. A month tells you immediately. You see the gap where last week went wrong without clicking into anything, and you see it as a shape rather than a number.
That shape is the whole argument for this layout. Four empty boxes in a row is a fact you cannot argue with. A completion percentage of 71% is a number you can rationalise all day.