A: The holders for the shofars (CBD Stock Numbers: WW452290 and WW452940) indicate which sizes they fit best.
Most people who buy shofars use them as decoration; because of their genuine construction, they do require practice and acquired skill to play adequately.
It is possible to find some instruction on how to play them online.
There are two major factors which determine the ease of use.
The first is diameter of the mouth piece, and the second is the length of the horn.
The wider the hole in the mouth piece the easier they are to blow through, but sometimes the wider hole is less aesthetically pleasing.
Very short horns are harder to make sound, but very long horns are harder to blow through.