I love kickboxing (I'd do just that for my cardio, if I weren't concerned about cross training and overuse injuries). But my 20 some Tae Bo workouts haven't gotten a lot of use. I get frustrated with Billy's uneven counting (2 sets of 8 on one side, 5 sets on the other, and sometimes he never gets back to doing the second side.)
There are also some double-time moves I find too fast and not necessary.
I've gotten rid of some of my Tae Bo's on Ebay, and I'm thinking of going through the rest and getting rid of only the ones that I like (the ones that don't make me yell at Billy!)
Kickboxing is a great exercise, and if you like the workouts, then deffinitely keep them. Sometimes you need a break from the same instructor, and it's good to have variety. Of course, if you don't like them for any of the reasons I mentioned, then get rid of them.