Only problem I see with metal is when the wires get very old or you have some naked wires in the conduit that could touch, which you shouldn't, plus the wires are already in there own rubber covering. Codes have changed over the years and the most important thing is to be up to the correct code for your insurance, so if something did happen your covered. Back in the days when I use to run electric wire, metal conduit was all we had to use, but that like I said was many years and codes ago LOL