I have the disk (but the inflator broke, then I bought a basketball inflator...and never used it) but then I inherited a bosu so I just used that instead. I would say it mostly worked but I was NOT comfortable jumping onto the bosu in the aerobic sections.
With that said, I didn't much care for the workout and the aerobic sections were poorly cued and very confusing
(admittedly I AM choreographically challenged, however I can usually master Firm aerobics, even the dancey ones).
The strength and balance sections were pretty good though, IIRC