I wouldn't say that mono people don't go through the "What is your opinion of him/her?" phase before they decide to give a relationship a serious try. Meeting the partner is something like meeting the family or friends, it just (normally) happens much earlier in a poly relationship than in a mono one. Because the partners is more involved in everyday life on every level than the parents or siblings normally would be. Not in a decisive/veto manner, but I think that it is in a way some kind of codetermination as the life of the spouse is or can be highly affected by a metamour.
And don't get me started on the maturity/sanity tests
One for each relationship, one for each parent (I hate it when children are part of the personal mess of people who aren't able to handle their lifes); and this is regardless of the way the relationship is build or the children are received. I never understood why someone has to proof that he/she would be a good parent if an adoption comes into play and there aren't some kind of mechanism for raising children in any relationship/way out there.
Facts: 30, female, bi, v-type relationship with Sward (husband, straight, mono) and Lin (boyfriend, straight, mono), poly-fi and co-primary.