I have been very pleased with the covers (Air Flow) and have used them for nearly a year now with both my boys (2.5 & 1). They are so much better than other types I've tried - especially the cheap PVC ones which seem good for a few wears and then if they haven't torn, the elastic goes and you get leaking etc. My only disappointment has been when they stop being water proof, but I was told to only expect them to last for 4-6 months and I still think they are better than the other types, and some have lasted for longer than that.

I had one new pair which was leaking (not waterproof) and rang up Louise and explained my problem. She promptly sent me out a replacement free of charge and I haven't had any problems with that one.
Overall I have been very happy with the quality of service from Nip Naps and the promptness of receiving orders. I intend to continue to use the products - including trainer pants (which are easy to use and more absorbent than others).