Buying a "sub-brand" item like this is something I think we all experiment with from time to time, hoping that we'll get the "good one."
If you are carrying school books, clothes to the gym or want something to throw in the car just in case, then this is probably the bag for you. If want to trust that the stitching won't come apart when when you are 3000' up on your favorite hike or that it will support the extra weight you throw into it, then spend the extra $$ and buy from an established brand.
As for the 5.11 72, I have one that I got earlier this year in trade. I haven't put many miles on it, but it was pretty well used when I got it. I got it for two functions. To store extra gear in my car and to use as a civilian travel bag. This past Summer, I fit a weeks worth of Summer clothing into it with room to spare during a family trip and it's gone camping twice to use as a base camp bag. It's been comfortable to carry with about 35-ish lbs., I'm not too sure I'd want to use is for any extended hiking. There are some pretty good reviews of it on youtube.
I keep hoping that some of the .mil pack makers, will come out with their .mil packs, but in civy colors.