In reply to Ryan Parle:
I'd return it if it started breaking that quickly.
My family has three TNF-style duffles, but all of them cheap(ish) models. The oldest is maybe 15 years old and came from a Nordic sports chain so not much help to you, but second one was from Decathlon, and must be at least 10 years old now. They have been used for carrying all our stuff when flying, I would guess at least 4-5 times a year, along with loading up in the car with camping gear and that sort of stuff. They are both still in perfect working order if a bit grubby. My wife just flew to Finland today with my younger son and they took the oldest of the duffles again as their hold luggage. The third one I bought from Aldi maybe 18 months ago, it hasn't been used so much for flights, but still gets loaded up with holiday stuff and chucked around campsites and stuff - and its fine, can see what could go wrong with it.
Look for bound seams, straps that go under the body of the bag and big beefy zips. Glad I never paid loads for a TNF one when my 15 quid Decathlon one has been perfect and even the 8 quid Aldi one seems great!