I have not tried them yet but will soon as a mate has a bumper to try them on. But the bracket i have printed has exactly the same fixings dimensions as the ford replacment part. It is made from plastic and due the the thicker wall sizes i have done it is far stronger than the ford one.
If done correctly 3D printed parts are as strong or stronger then an equivalent ABS part( as most of the Ford parts are). One thing i do is test the parts and break them.
I do clips for the side skirts on the sapphire which are very strong, better than the Ford ones. They are not unbreakable as they are plastic after all. I have put a lot of work into the things i have made, but unless someone has £0000's to invest in setting up the injection moulding its as good as it gets.