Which is better, a metal made one or a hard plastic one?
Have any of you bought the 100 yen metal tire lever tube repair kit at Daiso? If so, are they safe to change the tube without destroying the rim?
Personally I have never used metal tire levers. Aluminium rims are relatively soft, you don't really want to dent or scratch them with anything hard. Tires are relatively easy to get on/off, requiring nothing stronger than plastic levers (depending on the tire and how new it is, I can often manage with my bare hands).
The big variable here is how tight your rim/tyre combination is. Tight and your levers will matter. "Normal" tightness and you mightn't need levers at all.
The advent of tubeless tires and tubeless-ready rims have led to more combinations that are super tight. Ditto what kiwisimon says about pinch flatting if your combo is tight.