The straps on Deco slides come on and off, allowing you to swap in different straps on the same pair of soles.
If you don't already have a pair of Decos, you'll probably want to select the "Slides" option:
this includes soles and straps. If you do already have a pair, and just want to buy new straps that you
may swap in, the "Straps only" option might be for you.