Both are awesome & quite similar, but different too!! Plyo Legs is 30 seconds (about) of plyometrics cardio followed by 12 reps of a leg exercises (with moderate to heavy weights). Cardio Blast Legs is designed the same way, however, the cardio segments are a bit longer and somewhat more like a combo. For example, in Plyo Legs, Cathe might do 30 seconds of air jacks, in Cardio Leg Blast it's 2 plyo jacks followed by 4 air jacks 8X. Also the weighted exercises are more reps too in CLB.
Here's the other thing, if you buy the DVD you are getting more with CLB....there are tons of premixes on there, in addition, a core workout and the 100 Hip thrust Challenge.
They will both work you, I love them both...but since I am doing CLB now I am loving it and it is super fun!!!