I have applied 303 to the leather seats in my car without any adverse effects to the leather. The leather in my car is clear coated, not sure if your furniture would be.
On clear coated leather, the 303 did give the leather a pretty high sheen, just so you know. It may also make the surface a bit slick for a short period of time.
Overall, I really do like the effect of the 303 on leather. Also, the back of the bottle does say that it is safe for leather. :bounce