Who knows? Maybe he'll buy it and decide for himself that it's junk. You'll have the satisfaction of knowing he should have listened to you.
JESUS! (first time in years I have used his name in vein) Has it ever occured to you that I might just be using this for something different than what shells normally do? I might not be putting a coin inside the shell. Have any of you thought of reinforcing the shell? edited, Stick a piece of wax or something in there and keep it so the real coin can protrude just a little bit from the shell and you can actually grip it.