Hi I think it's a good plugin with very good potential and I consider in the future buy it but I thinking that possible add functionality except "Promote listing" like make listing premium and "Move listing to top". I think that possible to add functionatlity like "leader of.." leader of city, leader of rigion/(state), leader of country and etc. If city is very big like New York so it can be possibility "leader of neighborhood/quarter" too.
About the expiration, minimum 5 minutes , maximum 30 days. Why only 5 minutes?! Because can be areas with high demand , that very big number of people whom whould like to promote their ads in this particular area.
I thinking it's a great idea to let to the owners of classifieds websites to earn more money.
Where is location of "LeaderOf"? Aside of right or left. It's depent if it's LTR or RTL webside .
Thats all...