I haven't personally seen any of the UU kits, but I've read a lot of reports from customers and conversations back and forth between Mark and customers.
The consensus seems to be that they are good shooters for the most part. There are some lemons that squeeze through though, and fit/finish is not like their complete rifles. Mark's excuse is typically something like, "If you wanted the legendary fit, finish, and [under promised - over delivered] accuracy that Larue rifles are known for, then save up and buy an actual Larue rifle over the UU kit."
My actual experience is with two OBR's from 2010, one tOBR that a buddy of mine got last year, and two Stealth barrels. I've been very impressed with all of these. It's almost as if the bad stories that you hear about the UU kits are from a different company.
Take all this for what it's worth.
I'll probably end up with a tOBR ordered before 2020.