I have both the Dune HD Homatics Box R 4K Plus and Ugoos AM6B+.
If you only want to use CoreELEC to play DV material, the Ugoos is definitely the better choice because it can now play profile 7 with FEL and the Dune cannot. Audio-wise they are the same (in CoreELEC that is).
Advantage of the Dune is that it has Widevine L1 support, allowing it to use the various streaming apps with 4K/DV when running Android. The Ugoos will not do that.