My cat loves these but because somebody has decided they should now be a third the size they were she doesn't chew them so they are not effective at tooth cleaning any more.
These M&C Breath and Dental Care treats certainly work for smelly cat mouths! They are well received too, so obviously taste good to the feline palette. As long as potentially serious causes of smelly breath (i.e. digestive or dental disease) have been ruled out by your vet, I would recommend this product. Doses of 2-4 bits per day are most effective. However, unless regularly given, smells do return quickly in my experience.
My cats have had dental problems and needed veterinary treatment a few years ago. My vet recommended a regular dental regime and I get several products from VetUK for them as they're much more affordable than from the vets. I tried these treats hoping my two fussy boys would enjoy them and get clean teeth at the same time. One of them refused to eat any, the other one liked them at first but unfortunately went off them after a few packs. They're a good idea and would probably be fine with less fussy cats!