They'd still need software to control said hardware. We can assume such software would be mobile, based on what they're currently offering. Then they'd need a

They'd still need software to control said hardware. We can assume such software would be mobile, based on what they're currently offering. Then they'd need a way to pair the phone with the controller, or otherwise get the data over. This complicates things for the owners. At that point, you might as well just use the phone itself. Mind you that this limits the versatility of what they're selling - you can only print something as big as your phone - but they aren't aiming at the high-end market with this.