I'm thinking about buying the high step topper and getting rid of my blue and purple fanny lifter. I already have 6 risers so it would save me some space. I still use some Firm workouts though (new and old), and now Fitprimes and Kickbutts. Can I use the high step in these workouts? Is it easy/fast enough to adjust during the Firm workouts going from 6 to 8, 10, 14 inches high? Is there a difference between the blue and grey one?