I have the Stainless Steel Rescue Jr.
I have mine primarily as a collector piece since my boating and diving (snorkeling only) days per year are pretty limited. It is a good tough blade, and the tip is basically designed to be used as a pry tool, so that pretty much differentiates it from any other Spydie. If you carry a multi-tool with pliers, you may find that the prying feature is not much used.
I could be just as happy with an even more "junior" size, like a 2-1/2 inch blade.
For heavy-duty box destruction and pure serrated-edge cutting, I generally prefer one of the Harpy series knives to the sheepsfoot design of the Rescue series.