Great post, as it affords me with the unique opportunity (first time ever in history?) to argue that one of the 5.7x28's advantages is that it is so inexpensive!
(1 round of Underwood 9mm Luger +P 68gr Xtreme Defender costs about twice as much as a round of factory FN 5.7x28. Go figure!)
And the 5.7-28 cost way more than 22mag that some think is about as good from a small bore handgun . Not me ether .
Now remember the 5.7 is not a hot rod fired from a pistol and does not give you the same tissue damage as it could cause fired from a longer barrel like even with a 10" to 16" barrel . You also do not have the lower cost ammo like with a 9mm normal ammo lines does for normal range use But you will have that cool factor with a 5.7 ,, well for a little while .
Hope some of you early buyers know as beta testers don't run in issues found with one other m&p newer pistol . OH have you priced 5.7 better defensive ammo like speer gold dot ammo lately $$$ . Go Figure is right . But then it is hard to put a price on defensive ammo right ? The so called Hyper performance for the 5.7 is still only when its fired from a longer barrel than the current bunch handguns .
I stay with a heavy and slow 45 or a 155gr 1300fps 40sw . Enjoy the 5.7 - Honestly enjoy