Practice a ton. Grinding is still something that takes practice its not just the blast or finish. I average anywhere from 5-6 seconds on any metal yoyo (finger grind). You should see my throwhand index finger. Its really worn down from string rubs giving a nice coarse’esque type feel and yoyos love it! And on homemade sanding that works fine. I grind my plastic chaser and get 4-5 seconds on that.
People satin metal yoyos quite frequently to improve the grindability, but yes, it does radically alter the finish, which will affect the resale value.
Some even come that way…
such as the Dif-E-Yo Bonechip, Tank & Cross Bones.