I don't think I've ever encountered a Vagrant setup that was flaky and wasn't just down to the Devs not actually understanding how to write a vagrantfile. In my experience, those who have hate for vagrant are folks who either didn't know how to use it, or were burned by others who didn't. It's a real shame as well, vagrant's a really good tool.
I trust that the people who provided whatever configuration it used knew what they were doing, but it was still incredibly flaky.