The handle is capable of holding up to 10kg due to it's “compliance”
While carrying heavy packages you may feel the handle bending. It is completely OK, you don't have to worry about it breaking or cracking
I printed mine in PLA since it is a strong and at the same time compliant material. On the photo you may notice cracks on the edges - that's because I was carrying 12 litres of water in each handle
The author hasn't provided the model origin yet.