I have been mining Pi since November 2019. Based on my experience I would say that the app is “legit.” However, if your question is whether the Pi Network and the Pi currency is legit the is answer is: time will tell.
The Pi Network has a white paper, which is available on the app, and it seems that the development of the app and network has been following the vision set out in this document. It is quite clear that this network has a long term vision and goal and that it is not just another quick scheme. At the very least this makes the intention of the developers seem legit.
Refferal Code : Amarashi
It's time to get your Invitation.codes account too 😎