This is just a short list of what a A5 notebook should be like in order to be the most useful to me
Lined or grid
I prefer lined for long form writing and dot grid for tasks.
Hardcover; because it is much more convenient when I write somewhere I don’t have a flat surface available.
At least two markers
I prefer three
The paper should be good; Leuchtturm1917 or Rhodia quality is the standard I expect.
And then I mean both paper quality and shorter dry time.