I think it would be worth it if you have the other GS workouts, just to complete the set. I do have this one, but don't reach for it often even when I do a GS rotation. I actually like B&G and LOVE Lower Body Blast more and do that one instead of GS legs. There's more of a fun factor with LBB, in GS Cathe is a bit more serious... which isn't a bad thing.
I'm also not a huge fan of extensive floorwork so that's another reason I like GS Legs but don't LOVE it.
I think it would be a great addition to your Cathe collection, so if you have the extra money I'd say why not?