Free night banner (stay for 4 pay for 3)
Guests do not know there is a special on if choosing a promotion like this
if they are looking to book for 2/3 nights they could realize that if they stayed longer they would get a night free - and value for money for their stay
Currently only those guests wanting a specific period (you have stated as on promotion setting) would not see its cheaper
Not really shown as a "deal" on the overall site so not worth going that route as you get minimal exposure.