I would agree with the "ugly duckling"! I am sorry to say, but in my hands that one would be in the scrap metal pot very quickly.
Yes - use it to gain some knowledge. I would soak in Acetone for a few hours to see if that loosens up the clag. If not, I would be tempted to try something even stronger. If it is heavy tarnishing or other environmental damage, it may require a mild acid to get through it. All on the basis that the coin as it standards is worth only the silver content, so you are not losing anything.