I have a KR 4 bag roller that has lasted a long time. I have had it more than 5 years, probably closer to 7. It shows no signs of wearing out.
The handle did break this spring, but I contacted for a replacement. After describing the bag and then emailing them a picture of the bag so they knew exactly which model it was, they provided a replacement at no charge. Also, KR said this was a difficult handle to install so they had me send the bag to them and they installed it, again free of charge. My only cost was the shipping.