comparing prices... R&S MXO4 is 15% to 20% less expensive than the new Keysight HD3 in Euros and seems to be superior in specs.
How is it "superior in specs"? The HD3 is a 14 bit scope and has half the noise.
If that's not important to you, then ok, but ADC bits is a pretty basic top level spec, and it really stands out when you do those competition comparison tables the manufacturers love to do.
The MXO4 has faster updating as a banner spec, but I'm willing to bet the HD3 will beat it overall operationally.