Well the rules have a "Warhammer 40,000" stamp on them, meaning they can be used in regular games. Since it says they are an Elites choice you should be able to take up to 3 of them. There is just the question of how your gaming group views FW stuff though, as some don't like anything not in the codex. For that reason it probably will see most use in apocalypse games as you suggest. Rules look pretty decent, although I can't help feeling the Nurgle/Tzeentch marks are the better ones.
As for the model, it does resemble a Warjack as you suggest, although I think when you look at the sculpted details and iconography it fits very well with other Chaos vehicles. Should look more 40k-ish when painted in an appropriate colour scheme. I'll be getting one myself as soon as I can afford it (so probably not for a while....)