insider
n
person who, as a member of a group or an organization, is able to obtain information not available to others 内部的人; 知情人. insider `dealing (also in,sider `trading) buying or selling with the help of information known only by those connected with the business 内幕交易.
I suggest that we ask users of this machine what they think about it. We can photograph them using it too. Then we can put their comments at the top of the advertisement in big print. We can bring in some humour too. People enjoy reading humorous ads.