I installed Tower 4 on a Droid Turbo to check out the app and review mission setup procedures on something other than my GCS. I was able to create a survey, but I couldn’t save until I installed 3DR Services, uninstalled Tower, then reinstalled Tower. I reinstalled from within 3DR Services app, but not sure if that’s necessary.
No current version of tower, solo app, or Solex app requires 3DR Services anymore (thank god!). You can uninstall that.