Brit Care Grain-Free Indoor Anti-stress

I thought I should give it a try since BritCare is supposedly a super premium brand sold at affordable prices. My nervous rescue cat had previously been on Royal Canin Calm, containing L-tryptophan and milk protein hydrolysate, which she responds to very well. Since moving to BritCare, however, she's been extremely hissy and swipes at the other cats in the house. Unfortunately this product isn't calming at all. The taste is alright, she ended up accepting it after a week.

Unfortunately, both of my cats have vomited. Even though they eat the kibble, they end up vomiting afterwards because of it.