What is the difference "FTP on the Go" and "FTP on the Go Pro" for iOS?
Looks like the main difference is that the Pro version is universal. That means it will work on iPhone and iPad whereas the normal version only works on iPhone.

From the website:


  
  Optimized for iPad, but also runs perfectly on an iPhone or iPod touch.
  View many files at once in the tabbed viewer. This lets you easily copy between files, compare, etc.
  Switch between browsing and full-screen viewing or editing with just a tap.
  Quick-scrollers let you scroll through files or folders super fast.