You can use your Yousician Premium and Premium Plus membership on as many devices as you need, as long as they meet the minimum system requirements. However, keep in mind that you are not allowed to share your Yousician membership with anyone else unless you have a Yousician Premium Plus Family Plan. In that case, you can add up to three more accounts to your membership free of charge. They will also be able to use their respective accounts on as many devices as they need.