I tend to be leary of generic products, and when it comes to something like my baby's diapers I'm even more leary. A diaper is something that needs to do what it should, and as we've all learned sometimes the generic product isn't as good as the name brand. However, I was proven wrong when we tried Kirkland brand diapers.
I was using Huggies diapers and when we ran out I sent hubby to the store to get more. They didn't have the size we needed so he bought what they had which was the store brand at Costco. I was hesitant but willing to try them. They work great! We got the 1-2 size which fits up to 15 pounds. They fit my baby perfect, we haven't had one leak with them. A box of 234 diapers is $35.99 which is reasonable when you compare brands.
I can't say that all store brand diapers won't leak, but I can tell you from my experience the Kirkland signature brand diapers are certainly worth a try!