I've been using Norton stones since I started this journey, and at the time, other than King there wasn't much available. Shapton and Naniwa came on the scene shortly after. I've been using a granite surface plate from Woodcraft with w/d paper for flattening. It works well but is messy and takes up space on the sharpening bench.
I've been looking at Stu's site and trying to decide whether to pull the trigger on some Sigma stones, but I digress. I am looking at the atoma plate for flattening. I have a coarse/x-coarse DMT, but I have used it extensively for flattening chisels, blades, etc. If I scrub it clean, can it be used for flattening, or will there always be the chance of metal contaminating the stone?