I bought a pack and dropped one in a drain that had an odor and a week later nothing changed. Put a piece of PVC on an elbow to simulate drain trap. It appears that after they get wet they get soft and collapse and as soon as you run water the go straight down the drain. Doesn't take long to collapse so there's no way they could last a month in the trap. Total rip off.
Bottom Line: Yes, I would recommend this to a friend