I recently switched my reward preference to Emerald Club "free days" because it didn't seem like I was getting much in the way of frequent flyer miles from my rentals (also, it seemed like National wanted to charge me for those miles). Low and beyond, I see in my profile that I have now earned a "free day."

I didn't see any rules for what I could use this rental for, so I tried to apply it online to an otherwise expensive one-way rental out of EWR. All they had left were minivans, and the code took an astonishing $350 off the rental, but still left me with $150 in charges. I can do that one-way much cheaper another way. But I was wondering whether this is typical, or do these Emerald Club "free days" work effectively on one-way rentals?

If they do, it would be a nice benefit because I usually only keep a one-way car rental for a day and they're obviously much more expensive than regular car rentals.