Sorry to hear about the guppies
Fish in cycling is
really hard on the animals. . . I don't know that I would have listened to the shop's advice and chosen Tetra, or how they could possibly be considered 'better than guppies?' I'd probably have gone with Platy if I absolutely
had to put fish in a possibly cycling tank. I've lost Neons to cycling issues before, and it made me very sad. . . 'still under warranty' is a good thing, it means you'll get your money back - but that won't return the fish's lives. . . I'd be inclined to return them until I was
positive that the tank is ready.
I hope they do well for you! Neons are such pretty little things. . . I would proceed as if your tank is still cycling, and do consistent frequent water changes to play it safe. Two weeks
isn't a very long time for cycling, and I. . . have doubts that the tank is quite there, yet. Without that nitrate reading, it's impossible to guess. Please be careful!
You should
definitely look into picking up your own kit to test your tank water. Even after the initial cycle, it's good to have a clear idea of what's going on in there. Test strips are inaccurate, and fish shops seem to always tell people everything is 'fine,' even when it obviously isn't! The Master Freshwater Test Kit by API is the kit most of us on this forum use.
Not intending to deliver a lecture - some things just have to be said - hope you understand! Best of luck to you and your new babies - looking forward to the pictures, and best of luck!