I have used these a long time ago. they do work to an extent.
there is a method you should try to use when using AC. make sure you turn it off before then end of the journey probably about 5-10 before your stop. AC freezes water particles in the air. frost start to build up on the vents and ducts, when you turn of your cars engine, then water melts, then with dust bacteria grows which gives off the bad smell. the AC cleaners put a cleaning agent (some sort of disinfectant) into the ducts/vents which kills the bacteria.
if you turn of the AC early, then the water melts but will evaporate from the vents, thus no bacteria grows. that's the method I use and not had issues yet.