Hi there,
The thing that makes Plyo Legs unique and unlike any other Cathe's lower body w/o's, is the plyo segments + weight work segments, alternating. Yes, hiit 40/20 is a good substitute, but you are missing the lower body weight work IMO. A good way to include both, would be to use any preferable hiit w/o (40/20, 30/30 or pyramid) and do your own weight work after each plyo segment. For example:
Tuck jumps
*rest
Squats for 15-20 reps
*rest
Air Jacks
*rest
Static Lunges for 15 reps each leg
*rest
Mountain Climber's
*rest
Elevated Lunges 15 reps each leg
ect...
So after each plyo from the hiit workout, you would rest for 30 sec or so (pause the DVD) do a lower body weight work of choice and then alternate until you've finished the entire hiit workout. Make sure the weights you use are challenging.
EVEN BETTER, you can download just 1 Plyo Leg workout. You don't need to buy the entire STS Meso 3 set.
HTH!
Natasha