This is not a terrible idea. It is a tool that makes it possible for people to either retrofit a newer version of Python onto an ageing OS or to develop for a specific older version of Python on a newer OS. If you don't need the features the tool uses, you shouldn't use it--I don't see why you're comparing it to virtualenvs, it provides completely different runtimes with a different engine and a standard library, and the ability to switch between those by just cd'ing to a folder with a .python-version file in them.