Hmmmm, interesting concept. It's always problematic finding a machine shop that I like to work with. One that will do it to my specs, or specs we talk about and agree on. I would be comfortable with a deal like this, confident that the machine work was correct. Some assembly required!
I prefer to do my own assembly. But I don't know how big that market might be.
There is a risk alright, people are much harder to dial in than engine parts.