They can work. You just need to be super duper specific with them in areas your not strong on.
Like my icicles, I can get my relevancy up on them for searches like "glass icicles" but larger searches...like "Christmas ornament" its much harder to get seen. So i use them for that kinda thing.
I also tend to run it only during the holidays, set up specific items.
Does it make hand over fist cash, no...but its covering its own cost plus a bit