After using this exact product many years ago, I decided to give them a try since I couldn't remember if they worked well or not. The reviews here on Amazon, seemed mixed; stating that it either worked well at eliminating odors, or masked the odor instead of eliminating it. In an attempt to perform some semblance of a scientific venture, I performed a "pseduo-experiment" to evaluate the efficacy of this deodorizer.

I have a fairly smelly pair of shoes that I wear when biking through the city. I received the deodorizers and decided to test them on this pair of shoes, since I could see how well they eliminate already-formed odors. I measured the distance from the shoe opening to my nose over the course of 7 days to see if the distance would decrease; indicating that the funky feet odor was decreasing. Also, I noted the distance at which I could smell the distinct scent of the deodorizers; indicating if the deodorizers were turning my shoes into a pungently masked mess. In both measurements, I removed the deodorizer from the shoe. I always used the deodorizers with the hole open to the largest setting. Here's the results:

Day 0 (I haven't used the deodorizers yet, so this is my control/standard):
Distance nose to shoe (funky feet scent) - 2' 11"
Distance nose to shoe (deodorizer scent) - null, I haven't used the deodorizer yet!

Day 1:
Distance nose to shoe (funky feet scent) - 1' 9"
Distance nose to shoe (deodorizer scent) - 0' 4"

Day 2:
Distance nose to shoe (funky feet scent) - 1' 3"
Distance nose to shoe (deodorizer scent) - 0' 5"

Day 3:
Distance nose to shoe (funky feet scent) - 1' 0"
Distance nose to shoe (deodorizer scent) - 0' 5"

Day 4:
Distance nose to shoe (funky feet scent) - 0' 6"
Distance nose to shoe (deodorizer scent) - 0' 6"

Day 5:
Distance nose to shoe (funky feet scent) - 0' 5"
Distance nose to shoe (deodorizer scent) - 0' 5"

Day 6:
Distance nose to shoe (funky feet scent) - 0' 3"
Distance nose to shoe (deodorizer scent) - 0' 6"

Day 7:
Distance nose to shoe (funky feet scent) - 0' 2"
Distance nose to shoe (deodorizer scent) - 0' 5"

Overall, they appear to have done the job! The funky feet scent has drastically decreased, and while the scent of the deodorizer has certainly increased, it appears to have leveled off at 5-6" from the shoe opening. Furthermore, the distance of the deodorizer scent drops to 0" when I'm actually wearing the shoe, since the scent is unable to escape the confines of the shoe interior! I'm pretty pleased with the product, but I can't speak on long term durability of the deodorizers (how long they'll last) or their performance in other types of shoes (my shoes are 90% all-leather, with only the sole of the inside of the shoe being cloth/fabric).

So all-in-all, the deodorizers seem to both eliminate odors (decrease funky scent distance) as well as mask odors (overpower funky scent with deodorizer scent). However, the former is drastically more noticeable, so 5/5 stars!