...Testing it out is the most practical thing to do.

[there's a flicker of upset at the thought of potentially chopping off an arm when he's already in the body somewhere down the line, but quickly shakes it off]

If you like the utility of having a metal arm but don't necessarily want to get rid of a flesh arm in the end, you could always try getting some kind of metal glove fitted too. It might be bulkier than you're used to, but that's also worth considering.