The redcord system is something I started talking about on page 20 of the Drive Mechanics sticky. Start there and scroll through all subsequent posts entitled performance training. In total I think there was 7 or 8 posts. Read and understand them all before doing the program.
at a minimum, you can perform all of the necessary exercises with the straps and narrow sling. the wide sling might be more comfortable for some users, but most will get by witht the narrow sling fine. My DD does prefer the "handles" vs straps for many exercises, and I would recommend them, for sure.