You'll be using about 80 gallons. Where I am, premium is about .10 more and possibly .20 at some places. That's~ 8-16 bucks total difference on your trip.
The box has a knock sensor, however I'm guessing at least one knock must be detected before it backs timing out, therefore, there is some theoretical damage from the one ping. Also, I have no idea how long the DME takes to re-adjust maps.
Given the long trip, there may be sections where you might want to get on it, or you unexpectedly hit a hill while you're loafing around in low rpm's with a drink in your right hand (if you have a manual tranny).
That said, It's a coin flip for saving $8-16 bucks. IMO, if it were me, it's not worth it because I like knowing I can wind it out whenever I want
