I was just on that site, rubbernecking. Wish I had an actual use for one. They are intriguing. So far I have resisted.
The trick is, to print an armature, cast around it in concrete, then remove (destroy if necessary)I need a 2-1/2" ID to 2-1/2" OD coupler for my exhaust system on the Jeep.
I sure wish I could just print one of those!