Quote from Capn Bloggs:
"Or just have the discipline to, as PF, only call something that is already on the FMA and as PNF, not call "checked" without looking at the FMA first... Pretty simple really."
With respect, although you are right to emphasise that it's vital for a call not to be made until the new FMA combination has been verified, there's rather more to it than that. Let me explain.
Firstly, as others have pointed out, the PF only makes the FCU selections when the AP is engaged. If it isn't, the PF theoretically orders what he/she wants and the FCU selection is made by the PNF (PM). That's why I avoided mention of PF and PNF in my post.
Secondly, it's unnecessary and counter-productive for both pilots to speak following the FMA change. The only one who should announce the FMA change is the pilot who did NOT make the selection.
The pilot who made the selection carefully verifies that the FMA change on his/her PFD is in accordance with what (s)he wants, but there is no need for him/her to make a call. There are two reasons for this:
(1) otherwise it discourages the other pilot from taking time to check it properly on his/her PFD;
(2) both pilots calling adds to the plethora of noise in the cockpit (and the brief expression "checked" is so ambiguous as to be of little value).
Remember, as you imply in your post, the pilot who has made the selection is always, by definition, content that (s)he has got it right. Putting the responsibility on the other pilot to make the call:
(a) gives an independent verification (a second opinion);
(b) forces the other pilot to remain "in the loop".