Help me sharpen this knife

I was about to purchase one of these King 1000 grit whetstones: https://www.amazon.com/KING-Grain-Sharpening-Stone-Medium/dp/B0016VC46A

However, the salesman told me it is only good for carbon steel. That stainless steel takes forever to sharpen on this kind of stone. If I have both stainless steel and carbon, he said, I should get a ceramic stone. I just wanted to verify with you all to see if I understood correctly.