It's abrasive. So use it too much, and you'll be regretting the fact you ever found it. Leather cleaners always get the shine out and restore the matte look for me without being abrasive.
BTW stop conditioning your leather, that's probably why the shininess was there in the first place. Remember that you are dealer with a topcoat on the leather, and not the leather itself. Just like how you don't try to revitalize the color coat through the clear coat on the paint, you do the same with the leather. Use a cleaner that leaves nothing behind and wipe the seat down with distilled water after for good measure.