Baby Mum-mums (teething biscuits)

My little guy is 4.5 month old. He already has two teeth fully broken though, and a third on the way. He is doing good with cereal and puréed veggies, and can hold his head up great. A few friends with babies the same age as mine are giving them baby teething biscuits (Mum-mums). By the box standards and requirements he can have them, but I'm just a little hesitant. Any moms start their babies on these?