What is the difference between this and and the approach taken by eggs/buildout (other than the time difference, and so some changes in APIs)? My impression (ha

What is the difference between this and and the approach taken by eggs/buildout (other than the time difference, and so some changes in APIs)? My impression (having never used buildout) was handling multiple versions made debugging hard, and there were lots of random issues unless you did everything correctly (and that setuptools and its variants switched away from the options to use multi-versioning because it was effectively a foot-gun)?