Brett...The advantage would be to know your AR inside and out and get a better understanding of what makes them tick. If you assemble your own stripped lower you get to see how a trigger installation goes. If you chose to upgrade your trigger down the road, it will be a snap. Plus, there is a certain amount of pride you can take from firing a weapon that you partially assembled. I am not quite brave enough to assemble an upper with headspacing issues and all...Maybe some day.
I purchased two of those lowers from PSA...They are a good place to deal with.