The BE-3U uses liquid hydrogen as does the BE-3 instead of liquid methane; which, though hydrogen is more efficient necessitates a significantly larger tank for the less dense fuel. Perhaps the combination of the two much less powerful engines will allow a testing operation of a second stage with little to no payload; and, provide Jeff Bezos a photo opportunity. Washington Post can write about their owner and his space venture Blue Origin.
ULA wanted the BE-4 and partially funded it’s development for their Vulcan rocket. Apparently vacuum restarts were an issue for the BE-4U, which raises a question of BE-4 first stage engine restart also, as considered in the context of maneuvers of a reusable first stage.
Interesting.