You certainly can!
Simply Piano and Simply Guitar are available on mobile / tablet devices (we do not have a desktop version).
Once you install the app on an additional device, make sure to press the ALREADY A MEMBER button on the opening screen of the app.
Then, enter the email you used previously, in order to continue.
Have more questions?
Chat: In the app, tap on Menu ☰ > Settings > Have a Question?
Email: piano@hellosimply.com