Question Compatible USB CF reader

I was hoping that I would be able to connect my Canon DLSR 40d directly up to the HTC One but I get a 'device is not supported' message. I'm guessing the 40D is too old. So my next option is a USB CF reader connected to the phone. Does anyone know of a CF reader that would be compatible, rather than just taking my pick on an ebay special! Does anyone have any thoughts on if this will work?

Thanks in advance!