The way I look at it, one is a signature LaRue rifle. The other is a rifle assembled with LaRue parts. It was simpler back when the parts were part of the stealth line. But the “stealth II” line of parts does look a lot more like signature rifles, plus there is the assembly option on the UU (aka stealth II)) uppers.
FWIW I have a OBR, PreditAR, and 2 UU’s and an embarrassing pile of UU parts. The main problem I have with my UU’s is several are sbr’s and I have not gotten around to engraving the lowers - hence they sit as piles of parts. My OBR is a 308, so it a bit heavy. I have both a CM and a Grendel assembled UU rifles - the Grendel was part of the IPO, and is damn accurate. The CM is waiting to be sighted in (sad, sad, sad). The SBR’s are 300BO and 5.56-I wanted one in every caliber...
—-
There are several differences with the OBR. In addition to the cant, the back portion of the rail has been milled out so the BUIS does not have the extra rail cant. That happens to be an issue with me because my IR Hunter has an odd scope mount that needs to be mounted reward, and the OBR rail is shortened for the BUIS.