Rumoured to only cost $20 (at UK event so possibly £20 although even that seems unlikely). The image looks like the back of the box to me. If true then that's one hell of a cheap way to get hold of a lot of universal core cards.
The two Warband decks are "normal" sized (20+12). All cards in the Warband decks are Warband-marked, there are no common cards in the box. But the warbands are totally compatible with other Underworlds products, and you can also customize these warbands with common cards from other Underworlds sets, etc. They say a few different times in the rulebooks how everything is compatible (like for example the ghosts say they can move through lethal hexes, and Dreadfane doesn't even have lethal hexes).
Instead of the "choose a board, put 'em together", board placement is roll-off; winner picks which side of the board to use (it's double-sided), then other player picks which edge/side of the board to deploy from.
Hazard cards (the big ones with the red backs) are drawn at the start of each round. 1 is drawn at the start of Round 1, 2 in Round 2, and 3 in Round 3.
Other than that, it's basically the same as normal Underworlds. Oh, and there's a comet and a monster with hex markers that are placed/triggered by Hazard cards.
Lovely. Just remember that if you're going to any tournaments you cannot use these gangs in countries they haven't been released in yet (so they're technically only tournament legal in America and Germany right now). Even so the Sigmarines would make a blatant proxy for the original Sigmarine gang for Shadespire (leader, person with shield, person with two handed weapon).
The lady does have two options. Helmet or bare head. Most bare headed Stormcast have a helmet option as well.