fluwoebers, who must be in one of the SOCOM units, has written a must-read review of the FN SCAR, both light (5.56mm) and heavy (7.62mm) models.

Reciprocating Charging Handle
I remembered to keep my thumb down most of the time, but while practicing switching back and forth between strong hand and week hand, the charging handle caught me.
My thumb slowed it down enough that it caused a FTF.
It was not painful enough with 5.56 to learn my lesson.
I did it again with 7.62. That hurt.

…

“Softness/Brittleness” of plastic
The polymer is very dense.
It is a little on the soft side, so it is not likely to crack very easily.
It is not so soft though that it bends or deforms easily.
It feels like a pretty good balance in strength and rigidity.

…

Bottom Line:
The SCAR is a good system. I’m not ready to give up my M4.
As the SCAR evolves over the next couple years, it will be a top-of-the line rifle.
I’m not convinced that it is worth the cost to purchase and train on a completely new system.

I highly recommend reading the whole review. It is very comprehensive.

Big thank you to Jay for emailing me the link to the review.