It really depends on what you want out of it. I have the whole set and I just completed STS for the 4th time. I've done it using plyo legs and using squat rack legs and once in awhile I'll toss both in the same week. It just gives you more versatility. If you don't like straight lifting than squat rack legs probably wouldn't be something you would miss. It's four different exercises repeated four times with 3 minutes in between. Very traditional weight lifting. Plyo legs alternates between a plyo exercise and a weighted exercise and the weighted exercises mostly have a cardio base to them, so it's a much faster pace.