It would depend on the image you are engraving also, I tried for high detail on a completely "grayscale" image but I think I could have doubled my speed and power output and would not have lost too much detail once I figured out what made my edges seem blurry. Slate is quite forgiving also I guess since you can just sand it down although with these floor ones the lighter slate is not too far from the darker surface, each material will have its quirks.

Metals you might need to get a marking spray, stainless steel is the only one that has some kind of natural reaction to the diode laser, all the others you need marking spray and even then it might be best with a co2 laser , I think it is possible on diode but will take a bit of testing. All else fails if you can coat the metal first then remove coating with engraving then that is always viable I guess. Only metal I have tested was a pair of nail clippers for stainless steel and anodized aluminium dog tags. No clue about PCB , might be similar to acrylic so maybe you can cut it and even engrave with Diode (budget) likely definitely co2 and fibre.