i have the 4n1 b/c i figured from the clips that his style was going to be slightly different then other barre workouts. i say if you have a sense of barre workouts then this is another good one to have. the pace makes it cardio like and you have to keep control. i haven't done past beginner personally b/c i am just afraid to go up. i find beginner workout comfortable right now.
the cool thing about 4n1 is you get an instructional,more slower pace of the workout, beginner,intermediate, and advanced. so you can progress without having to buy another dvd(unless you make to inter/adv then you can buy his ultimate advanced workout which has a long total body workout, lower body and an upper body/abs workout but i don't have that one).
i don't have p57 but i see similarities just basing it on the clips. cardio barre also does some traditional floor work like leg lifts and pilates style ab crunches.
kassia