It doesn't work for me. If I remove product weight, Prestashop doesn't know what prize range should it use (Royal Mail Large Letter has 4 ranges - 0-100g, 101-250g, 251-500g, 501-750g) and then add all the products into the first range. For example: I can order 5 items without product weight (300g in total) but Presta picks 1st range (0-100g) which is also the cheapest.
Any other ideas? Maybe some modules?