Which BusyBox is legitimate on Play Store?
Use either of these:


BusyBox
BusyBox Pro (paid)


Note this comment in the description:


  Please note I did not write BusyBox! I wrote this installer and cross
  compiled BusyBox for Android. Please see the about menu option for
  more details or here: www.BusyBox.net


If you're installing a custom ROM, it might have BusyBox already (but usually not Pro).