I use my Fanny Lifter as a computer table. While it works well for that, I wouldn't recommend using it instead of the High Step. It's definitely not as sturdy for working out as the high step. The FL is lighter, and can easily scoot away from under you if you happen to hit it (something that could easily happen with some of the fast toe tap moves that are in the High Step workouts). It's also not made for impact (and somewhere on it, say do not leap or jump on).
Before I got the high step topper, I started using my regular step turned vertically (and bought extra risers to make it go to 12").
I highly recommend the High Step topper over the Fanny Lifter.