I used Penofin Hardwood Oil on my Ipe' deck and it was a huge disappointment; didn't last 6 months before turning into a muddy, moldy mess. So if that's the same stuff you are considering I recommend you reconsider. Any finish requires maintenance so I think you should reconsider the film finish as it will provide more protection than any penetrating finish and ash needs as much protection as possible to survive outside.
John