In October 2015, I bought two packs of five from Diver's Den. About five died within the warranty period and another two died within a few weeks. One died a little more than a year after purchase. The last two I still have to this day.
Late last year, I bought another two packs of five. Pretty much the same story: three made it long term. So I still have five Cardinals in my 40 Breeder.
My luck hasn't been great with them, but they're so cool, I'm going to try to keep replenishing them. Not too easy since they sell very quickly on DD. They seem to be fairly hardy once they've settled past the first few weeks. I think multiple feedings really do make a difference--I feed thrice a day myself.