Welcome to TFP!
I don't know the Nautilus, but I know the M5. I can promise you it will not damage the finish in your pool. Actually the other way around. While the PT finish won't damage the cleaner, it will wear out the contact points such as tracks sooner than some other finishes. I think people have had good luck with the Nautilus, and my small experience with Dolphin products has been very good.