I started onion and leek seedlings this way two years ago– it’s very convenient because you can simply unroll a section and take out as many seedlings as you need without worrying about damaging or exposing the roots of the remaining ones.. The taller the spiral, the better the roots develop. The only thing I’ve noticed is that the soil dries out faster, so you need to keep an eye on it and ensure there’s enough soil in each layer.
