The thumb rest makes a one handed hold much much easier. I can't wait to get it to the range and shoot it. We already have one of the stainless Mk3 Target's. It's a really fun gun. I'm thinking that the competition will be a good companion.
The biggest issue with assembling an AR isn't so much getting the parts together right - it's getting the right parts together. You'll remember the quality of a gun long after you forget how much you paid for it.
US Army 1966-69, VFW Life Member, Retired Geek