Keyboards give you the ability to move around from room to room, more so than your standard piano. This gives you the freedom to be able to set up and play in whichever room your computer is in.
Keyboards can also produce a variety of sounds and this can add to the fun of playing music. Something to be wary of with keyboards is the total number of keys and how these keys are set up. While full sized keyboards will not present any problems, smaller keyboards (67 or more keys while good to start on, are set up slightly differently – instead of middle C, F is in the middle of the keyboard and this might be a little confusing. It does depend on how serious you want to get with your piano playing and you just need to be mindful of the differences when going from your keyboard to a full sized piano.
While Rocket Piano is designed with piano players in mind, keyboard players will still gain just as much from the course.
Conclusion: Good to start on just be mindful of the setup differences.