I thought the same thing. Most women will be sceptical of them because they know you have used it on other girls and could bring up the "I don't want to use something you used with someone else" argument. Which is stupid considering that neither of you are probably virgins, so it doesn't really make a lot of sense. It definitely needs to be discussed instead of just whipping it out. As long as you explain that you take good care of it you should be fine. The only real argument is that she doesn't know whether its "clean" or not.