Okay~this could just be MY take on it, but.....
MIS (legs) is slower paced, more of a strength/muscle building video and you can adjust your weights up and down as necessary, staying light or going really heavy.
Leaner Legs (which will always be Meaner Legs to me) is much faster paced, and I don't believe you'll go but so heavy on this video only because of not only the high reps, the fast pace. I usually use a 40#bb, and I find my heart rate racing throughout the whole workout. By the time the abs section comes I am actually saying, "wooohooo, abs!" And unlike most leg workouts, I always feel leaner Legs the next day! There are no breaks like in MIS for stretching, Cathe works the opposing muscle group instead and calls it active recovery.
Both workouts are wonderful in their own unique ways and you wouldn't be sorry for purchasing it, it is a killer leg workout!
Donna