[Daryl]

I have been told that one can let the right wrist flatten after impact if you swing with the right arm as opposed to keeping it bent with a left arm swinger.
If that is true then the challenge, would seem to me, to make sure that it doesn't straighten until after impact.

That's correct. Set-up with the correct amount of Left Wrist Bend and Right Wrist Bend for the Club Choice. Maintain that degree of Left Wrist Bend Throughout the Swing.