Wow this is a great hackathon project. It's simple, but something that people will actually want to use after the hackathon. I do agree that the message may need some tuning up though. Maybe say "John is using anonysize.me to ask you for your size" etc. It adds some credibility even though no one has heard of you, and it leads to brand awareness, advertising, and hopefully more users (this is just based on the text message on your homepage, however).