Protecting under a roof ridgeline for ember attack, both fibreglass type batt and a rockwool batt will perform adequately because there simply isn't the heat locally to actually melt out the glass batt.

If you were trying to prepare a roof for flame attack and direct like flame zone impingement, then the rockwool option would be a preferred upgrade.

Dektites aren't created equal, and you'll find that there's two types when you go into a hardware store. One is a high temperature one, which is actually designed to go around things like flues for wood heaters and gas heaters that perforate up through the roof, and they're typically a red silicon material. They're quite high temperature performing, and can resist quite a bit of debris build up against them, and the burning out of that debris.

You can clean your gutters out, but during the fire event itself the debris can build up again, to some extent in those gutters and apply localized flame attack to the roof elements adjacent.

Gutterguard essentials: Galvanized or stainless, aperture size 2mm or smaller, and fixing both to the roof and to the gutter line must be of some type of non-combustible material and flashing.