Is there a limit on how many times I can do the workout or how many times I install the app?
No, there are no technical limitations. You can install the app on your Android smartphone, on your iPhone and on your iPad at the same time and use it as often as you like (e.g. for your partner, …). You should initially train only 1 x a week with EMS, later you should keep at least 48 hours break between your training sessions.