For me best keys are mini hand saw blades right now. Metal saw blades didn't bent and braked easily.
I Snapped the saw blades half and made them safe for player. I tuned each key in right note with guitar tuner. I have seen that professionally made kalimbas have keys in different length. I think that moving key in different length under bridges etc. works same way as different length keys.
How important is bridges etc. distance between each other under keys I don't know right now.