How durable are the parts? I spent a few hours last night looking at options and the one that seemed to produce parts that one could use on a car
was the Solido SD300. This company seems to have gone into receivership though so I'm not sure about support and continued access to materials, etc.. Thoughts?
Most people print using PLA plastic, which is biodegradable, but easier to work with. If it's exposed to elements it would need to be sealed, otherwise it will degrade from moisture. Some printers can also use ABS, which prints at a higher temperature, is a bit finicky to work with, and releases fumes during printing. The advantage of ABS is that it's impact-resistant, and would do well for a car part.
In terms of use, these aren't what I would consider appliances - they require a degree of consideration for every print. The process itself is an art, since there are no settings that will print well every time, they must be adjusted from print to print, and material to material. In addition, a perfectly completed kit didn't print or connect right away, it required a few hours of troubleshooting.
On a scale of 1 to 10, my prints are about a 2 right now. I have had my printer for a couple of days, 2 for assembly and about 2 days of printing, and am still getting to know it. The hardware itself is extremely capable, here is an example of a high-res print using an Ultimaker:
http://www.hive76.org/insane-3d-printing-resolution-ultimaker-under-the-micro
That's at 76μm of layer height, but there are prints at 10μm (0.010mm) - I am currently printing at 0.3mm, or 300μm.