Dennison is rightly best known for the myriad of superbly designed boxed sets of seals, cut-outs, illuminated silhouettes and the like they produced from about 1913 through the 1960s. (The best of their production happened from about 1916 through 1930.) Some of their slide boxes are difficult to find while others more steadily become available. As this fine seller states, complete near-mint or better boxed sets are becoming harder to find. This particular set tends to be seen more than others and the guide value reflects this. These typically trade for $95.
Mark B. Ledenbach's vintage Halloween collectibles blog.