The cutting head is heat treated carbon steel and doesn't wear fast with normal use. I had one for 30 years and the spring broke, not the blade! I got my money's worth out of that one! This is one tool I sell that I have used over and over. I am a big nibbler fan!
The humble nibbling tool is great for cutting about any crazy size hole in plastic, aluminum and light 18 gauge steel. Custom car radio installers use them for enlarging to make things fit. If they don't, they should!
Side note--If you use it on aluminum save the little metal bits for your lab experiments...making hydrogen balloons, etc. We filled balloons as kids and watched them float away.
I included guitar work in my description but I understand from what I have read, luthier folk need to modify the blade to use these for their purposes. I threw that in for people like me who like to multi-purpose a tool to the max.