By no means a general rule, but my personal experience is that my saphir buffed shoe incurs less marking than when I'd used kiwi on it. Also, no issues with switching between kiwi and saphir, but I would prefer to start from scratch and remove the kiwi layers first.
I haven't found a product that can do this easily though. Mostly I'm advised to work the layers away using renovateur. I'm wondering if saphir cleaning soap might do the trick - anyone with experience?