I wouldn't get too excited. Its probably not as good an offer as you think.
They ran a similar promotion last year that if you stayed three nights, you got one free to use at another time. My DH and I had to take our daughter to college in Savannah so we arranged to stay at a Choice Hotel to take advantage of the promotion; we had to join their frequent stay program to get the points for the free night. Joining the program was free, so not a problem there.
Then after the points for the free night were awarded, they let me know all the restrictions. First, there were only a certain 'level' of property available for the free stay, generally the much cheaper option property (we wouldn't have even been able to stay free at the hotel we stayed at to actually GET the free night).
Then I discovered that a reservation could only be made 45 days in advance...so not much in the way of advance planning available.
I'll probably never end up using it.