You're welcome to use your Billdu account on more devices, just log in on the Billdu website or to a mobile app with your e-mail and password you've used to sign up. All your data will be synchronized. You can manage your account with the mobile app and from the website as well.
You can use Billdu with more mobile devices or with more browsers, there's no limit on devices you can use. Your subscription will be active across all devices.