Any PM who will sit passively and watch the PF make a complete hash of an approach just because he isn't doing the landing isn't doing his job and shouldn't be in commercial aviation. You both have "skin in the game" regardless of whose sector it is. If you have to fly somebody's approach to be reminded of that then there is something fundamentally wrong, I feel. Maybe I'm a rare example of a BA pilot who is completely underwhelmed by the monitored approach concept, the reasons why I have just given. Granted it does work well in low vis situations as stated (indeed I operated with those SOP's at another airline) but doing them all the time is a bit of a nonsense.