Highly subjective! They are mystical barbarians with swamp-corpse elementals, superior giants, ancient power stones, Old One relics/ weaponry, and their own list of items/ lore of magic from the TT rules. Plus they'd be very inwardly-focused rather than aggressive raiders, likely a "build tall" faction looking to improve their capital & achieve unique win conditions, rather than conquer the known world.

Also, most Albion natives would never align with the Fimir, as the Truthsayers are 100% opposed to Chaos (Albion basically exists to siphon excess magic from the north pole and support the Vortex in secret).

Everything I mentioned is of subjective as well (not everyone loves giants), but I'm just saying they have much more potential than just the Fimir. Considering they'd be another humanoid faction with giants, they could definitely be a Norsca-sized DLC, and also act as a foil for the Chaos Vikings.

Here is some art: https://imgur.com/a/OPMAN