I've had mine for 11years. They're a nice accessory to have on board as they're easily stored and as such can be left on the boat. However, if used a lot by themselves I could see them wearing out quite quickly. I also use 'sausage' fenders but they're quite difficult to get in the right place and as such can roll up and leave tubes exposed.
As such, in the interests of overkill I use both. There's been a number of times where the tube fenders have rolled up but the tubes have remained protected by the flat fender.
Guess what I'm saying is that I sleep better at night by using both and not relying on just one type.