Stop in for a cup of coffee

Mattax said
Not flat enough.
and harder to remove.

Might be OK on a standing seam, but I think it still might stick up too much with tin.

Lemme think where I have pictures or illustrations of how the tabs get nailed down.

Here's a couple showing stand seam tabs. Flat seamed is similar but IIRC the tab may be folded over the nail head.
from Old House Journal 1994 when it still had a 'how things are done' focus.