I have worked in a few "co-ops", and "collectives", and mostly in a union shops. The difference is all about power. Not pay. Not benefits, nor guaranteed employment.
When a "collective" works well, it is very flexible to the needs of the workers. It operates on a human scale. Decisions happen from the bottom up, rather than the top down.
You might be surprised how productive, and how efficient a "collective" can be. Just by removing the managerial level.
