I wore the Acerbis for my trip to Morocco, where it got up to 36 degrees. Worn over a sweat-wicking T shirt, with a Joe Rocket mesh jacket on top it was great.
Yes the screws come undone and I've lost one, so you do need to threadlock them.
Although they won't be as good at resisting abrasion as a proper leather suit, I suspect they would stand up pretty well due to the thickness of the plastic. Not tried it so I can't be sure!
I tend to wear it in the UK under my cordura jacket, since it has a good back protector and kidney belt.
Trouble with fabric jackets and built in armour is that it can move about, and may not be over your sticky-out bits when they hit the deck...