From the blurb
Across multiple rooms at normal listening levels, Reference 1 consistently sounded more transparent, coherent, and free-standing than Reference 3/5
I stumbled across the Reference 1, first in The Absolute Sound compared with big Quad elecrostatics, and secondly when my main dealer had traded in a pair. I snapped them up as a temporary replacement while I fixed my Quad ESL-2905 electrostatics, but in many ways they are better than the big Quads, if you have a suitable amplifier to drive them (and a subwoofer?).
KEF technical papers are highly recommended because they highlight the trade-offs made during the R&D process. Key to KEF and Quad ESL speakers from the 63 and later is their coherent sound source, in KEF's case from coincident drivers

