Onduline / corrugated bitumen roofing: better to use nails or screws for fitting?

I’m about to lay Onduline on a 25° roof and am undecided as to which fasteners to use.

Most guides seem to use the nails, and many don’t even mention the availability of screws.

In my mind screws will make for a better fitment, as I can carefully get each one right, and if I do over-screw I can always back it out. One bad strike of a nail with a hammer (or an unexpected soft patch of wood) and the fitment could be compromised.

I kinda assumed the nails are the goto choice because they’re cheaper and faster.

However, I now note that oddly the SCREWS are cheaper. In the UK its £7 for 100 screws or £18 for nails! So why aren’t most people choosing the screws?

Assuming both are fitted perfectly, which do you think would SEAL better? The screws have no caps but seem to claim that they don’t need them.

Screws: https://www.wickes.co.uk/Onduline-Roofing-Black-Screws-60mm—Pack-of-100/p/207693

Nails: https://www.wickes.co.uk/Onduline-Profile-Sheeting-Nails-70mm-Black-PK100/p/240085

Thank you!