I understand all the concerns about leg strain, but I believe that's to be alleviated by using lower weights than you normally would. For instance, for PLB I usually go 30, 35, 40 like Cathe does, but I will lower the weights to 15, 20, 25.
To answer the question about The FIRM, I took this exerpt from one of the websites I attached previously. This is a recommended rotation which includes Firm's Standing legs! Cool, huh?! Just some more examples. We girls have just got to get creative....
Advanced Video Rotation:
Monday: Cathe's Maximum Intensity Strength OR Firm's Tough Tape followed by Kickboxing video (your choice)
Tuesday: Firm's Sculpted Hips, Thighs, and Buns followed by cardio (your choice)
Wednesday: Cathe's Pure Strength Legs/Abs (standing portion) followed by cardio (your choice)
Thursday: Cathe's Pure Strength Legs/Abs (floorwork only) followed by cardio (your choice)
Friday: Firm's Standing Legs followed with Cathe's Pure Strength Back, Biceps, and Abs
Saturday: Firm's Lower Body Sculpting followed by Cathe's Pure Strength Chest, Shoulders, Triceps
Sunday: Rest, Yoga or Cardio (your choice)
By the way, I don't know about you guys, but I've been feeling my legs all day.