I've never had a nippy cardinal.
Anything will try to taste the fins of a fancy Betta, as they look like decaying plants. But even here, not a problem. I think it's a myth.
I bought 30 to add with the small group I bred here, and they are delightful. In big groups, they are amazing. The most I ever had at one one time was 300, but I used to love the wholesaler's tanks with 6000 in there.
I fall for the new and exotic trap sometimes, but I always have room for cardinals.