If you think Tarsnap is Dropbox with an open source client (but marketed differently), a) you do not understand the engineering reality of Tarsnap (or you have a very... curious understanding of Dropbox) and b) Colin, please note that your marketing is creating fans who think that Tarsnap is Dropbox with an open source client.
I think Patrick's comment still applies if you think he described "Dropbox with an open source client." Since it's still tarsnap, it still retains all of the security benefits of tarsnap. Saying "open source client" does not capture that.