Like LR said, it depends on the kid. You've mentioned before that your son gets attached really easily, and gets very sad when people go away. In your case, getting to know partners outside the home and then keeping them on a friends-basis with your son is a reasonable course of action.
My point is that the example doesn't make the rule. There is no universal script for "poly parents." What's good for you may not be good for other people, and vice-versa.
For some kids, it may be better to have their parents home more often and not out dating, especially if they're already busy with work and other commitments. For example, Auto is the working parent. Zoffee has anxiety and can't drive or go out much, so she also runs most of the household errands. She also does drag, and that takes her away too. At the end of all that, it would be more deleterious for her to have all her dates away from home, because it would mean even more time spent away from her kids. Because she's normalized the concept of "people come and go," her kids don't think much of it when the people in specific roles, i.e. casual partners, suddenly stop coming around. They meet their needs for stability and love and connection through their family.
Gralson: my husband (works out of town).
Auto: my girlfriend (lives with her husband Zoffee).
The most dangerous phrase in the English language is "we've always done it this way."