I tried it once...
...and didn't like it. I bought Maximum Cardio and thought in some ways it was good (at least it wasn't too easy, I hadn't discovered Cathe yet), the silly posing made me laugh and the dead-serious delivery was not much fun. I also thought the mansion set was a little silly, sort of like faux upper-class. I think the CIA sets are an improvement and of course, Cathe's latest sets are the BEST. Once I got CTX, it's been no looking back. I don't buy much other than Cathe now. I have found that I just don't use the others that I buy, I find my hand reaching for Cathe over and over again. It helps that she puts out such a great variety. The only exception is my yoga stuff, and I keep holding onto hope that Cathe will do that some day (pls let's not start another thread on that, OK?).
I think the essential difference to me between the Firm and Cathe is that Cathe is more real, more honest, more direct. There seems to be a lot of drama about the Firm founders splitting up recently and I like the fact that Cathe has no drama. She never says anything bad about other instructors/methods either (very unlike the Firm - their constant "we're the only game in town" is grating and not true).
Now I know some folks do Firms and get good results so I can see that it's possible to put together good rotations from their tapes and keep in shape. I respect that. I just don't like the drama and also their workouts are not for me, based on this one tape and also what I've gleaned from reading reviews on VideoFitness.
Meredith