On average, I have a harder time trying to introduce neons. They seem to be less healthy than cardinals on average. The vast majority of cardinals are wild-caught.
As such, they can be subject to considerable stress on the way from S. America to your aquairum. If they make the trip well, you should do very well with them. Once established they're actually one of the hardiest aquarium fish. It's not unusual for them to live for many years.
I've purchased groups of 24 with a 100% loss rate in two days. Many other times, I've purchased even larger groups without a single loss after a year. It's HIGHLY dependent on the condition of the fish on arrival. Acclimate them carefully, but don't dwell on it if they don't do well. It's most likely out of your control.