There is nothing wrong with coin gimmick as long as they are used with sleight of hand skill. A lot of the time they don't do the work for you, they just make what you do look more impossible and move less. Take a look at A lot of Troy Hoosers magic, he uses shells and other gimmicks. Yet nobody complains about that. Coin One. Come Fly With Me. etc etc. If you combine decent to good skill with the shell or gaff, then nobody will suspect anything. In fact they will be more likely to believe it was magical.