My last cocker, Jess, came to us on Beta puppy so I just kept her on it as like you I had no reason to believe there was anything wrong with it. In due course both she and Jonny (springer) went on to Beta adult with no problems for Jess, but Jonny developed terrible skin allergy. Eventually the vet persuaded me to try changing the food to Burns and the skin allergy disappeared. Jonny's been on it ever since. So the Beta was fine for one dog but didn't suit the other. Now Burns doesn't suit Penny as she couldn't keep weight on, so I changed her to raw, but Jonny stays on the Burns.
I think what I'm trying to say in a long-winded way is that different foods suit different dogs. There are better quality foods out there than Beta, as far as ingredients go, but it's up to you.