The top spiral binding is a small thing but it actually makes a difference when I'm sketching a quick diagram and don't want the wire digging into my wrist. Fifty sheets feels like plenty for a couple weeks of field notes, and the grid spacing works fine for scaled drawings.
The Universal pages handle both my quick notes and little scaled sketches without me switching notebooks. Fifty sheets is plenty for a month of site work, and the top spiral never gets in the way when I'm writing against a wall.