Do Air Adjustable Load Assisting Springs replace shocks?

We are needing new shocks for our truck (HD 1/2 Ton Silverado), and my hubby wanted to add another spring also.  That was the first plan.

Guys at his work said to just put on these Firestone or Airlift "Air Adjustable Springs" intead of either of those things above. 

I wanted understanding - we don't need shocks at all anymore?...or do we get shocks and this air adjusting spring deal he's set on getting? 

He seems to think no, we don't need any shocks along with those air springs, but nothing I'm reading about the products say that.