Yeah, from the picture it looks to be the size of the DF Leviathan.. While I think it's a great model I really can't justify buying it when I can simply drop $15 or whatever on a thermal cannon equivelant arm. Very nice model though.. I sincerely hope GW is on the start of a great trend that leads to more of this sort of thing.
EDIT:
I also presume Micro Art Studio and Blightwheel will be selling quite a few Ad Mech models in the next few weeks.