I don't cook turkey all that often, but the thermometer is good for chicken or other poultry, too. It's much smaller than the typical meat thermometer and also much less likely to injure your hand if you go fishing around in a drawer for a thermometer that you rarely use.
I haven't dissected a turkey thermometer to confirm it is metal that holds the spring, as opposed to some polymer, but assuming there is metal inside the thermometer, I'd recommend discarding any thermometer with a damaged coating. Metals with low melting points tend to be toxic, after all. This also means that if you cut open your thermometer to examine its workings, you should use care and dispose of your experiment out of reach of children or pets.