I met the Scrumbles teams at Crufts a couple of years ago after we got our cat, she clearly had a sensitive stomach and within a week or so on Scrumbles she was much better.
Unbelievably we recently got a rescue puppy who arrived with diarrhoea and underweight. The improvement he has made on scrumbles is huge. He is at a healthy weight with normal poops. Now he just has to learn some table manners!!