The SCAR comes in 2 different flavors, the SCAR-H which is a 7.62x54mm (.308) designated marksman style rifle and the SCAR-L which is a 5.56mm M4 replacement weapon. The L hasn't been tested very much yet, the H isn't being very well favored by the military people I've heard from.
Honestly I think they need to look into switching to the Remington 6.8mm SPC cartridge. The 5.56mm gets a bad rep and when it works properly it's great, but too often it doesn't work as anticipated. The ACR comes ready for the 6.8mm w/matching barrel and lower receiver ready to go.
And you can't trust everything you see on YouTube videos.
I think the 6.8 is a great round, however I see two issues with it. They really aren't problems per se, but worth noting. Ballistically you get more penetration with the 6.8 which is great when you're fighting through cover. However in CQB urban environments over penetration becomes a concern. Secondly switching to 6.8 would be a major hassle to change the NATO standard, and if you decide not to go that route supplies would be even harder to come by.
On a side note, I am pretty sure the "L" model is available for purchase, so there should have been more than enough testing.