Is there a reason to prefer one over the other? To be honest, the only benefit might be that the metal nail file will last longer. But I'm not endorsing emery boards either.

NL Metal nail file used in Harbour Grace armed robbery 35-year-old resident is in custody, police say CBC News · Posted: Aug 29, 2016 1:32 AM PDT | Last Updated: August 29, 2016 ...

Metal Nail Files Often made of steel, these tend to the most durable of all nail files and are therefore the strongest option for nails. A metal or steel nail file are best suited for those who ...

Wirecutter, a product recommendation site owned by The New York Times, recommends the Checi Pro Nickel Foot File ($26), which is metal and can be sanitized, or the Gehwol Wooden Pedicure file ($25).