You get some building pieces, but Cerberus gives you more. The scenarios included apparently have it so whoever wins the first one gets to use the SSU units that come in the box for the rest of the campaign, so they've given a way for Axis / Allied troops to use those figures.
I also only play Axis and Allies though, and have no plan on ever buying this set.
What SSU units come in the box? It's only Chef and the sniper character. Also Cerberus takes place in Britain. Can you clarify which Campaign pack you're talking about?