Re:
We've got it covered now. I used a printing that was beefed up about 50% on the 'wings' that go around the frame, the one on the far right in the foto. I brushed some rougher parts with acetone to improve the 'cohesion' of the ABS printing (this was done at 45% fill rate by the way, more will make it denser and more brittle). Acetone gives it a nice smooth surface.
Then I drilled the 12 mm hole slightly more to the centre, giving the threaded insert the same amount of plastic support all around. Brushed the inside with acetone to soften up the ABS before pressing in the insert, it becomes a push fit then (by thumb).
That's it. The hanger flexes quite a bit, but on the bike it behaves nicely. Like Confucius said: The green reed which bends in the wind is stronger than the mighty oak which breaks in a storm.
We have no plans to sell or produce more of these, any one can use the CAD drawings (gracefully supplied to us by Danson, dankjewel) and print their own.
It wouldn't be economical either to print hangers in Holland and send them to the UK.