Cable ties for securing the load!
Not something I would trust... I suppose it's nothing to bring along a whole load of spare ones... but there are good ones and bad ones.
There is very little load on the cable ties, in fact the assembly will sit on the stopped bike with none! The ties just stop the assembly bouncing off.
That tall rack as well as the particular load transfer point has greatly increased the cantilever length on the load bearing assembly... I would want to recalculate the maximum load on that system.
I don't understand why the height of the rack impacts on the cantilever length. But yes, with the rearwards placement of the panniers, loads on the carrier are high.
The load bearing bushes on my Birdy's rear carrier rack have failed - the flange part has separated from the barrel part on most of them. This increased the tendency to rattle.
I need to make some new ones and see if I can improve on the design.
Yes, it will be interesting to see what happens. Of course, with my bike having 2.8 times the rear suspension travel of the standard bike, the dynamic carrier loadings are vastly lower than they would be with the standard suspension bush.
[edit]: Is that stainless steel you are using? If so, where do you source it from? I am having difficulty getting hold of some...
It's chrome moly tube, nickel-bronze brazed. I am not aware that you can braze stainless steel, and in my experience, silver solder (that you can use on stainless) is much weaker than nickel-bronze brazing.