In January of 2019 I also listened to KEF’s LS50 and R3. They were connected to an Arcam amplifier.
I really liked the clear presentation and openness of both of these great looking speakers. The listening room was not optimal and maybe therefore they sounded quite alike.
Maybe all I can say of what I learned then, is that the R3 sounds a bit fuller. This must be due to the woofer in the design. Duh…
I started reading up on these speakers and found that the LS50 has a cult following. There seems to be another large group of people who find them too analytical or too thin.
The speakers are meant for my living room. It is not a big room, still I felt that the LS50’s might just be a bit too small and lack proper bass.
The R3 being a new speaker at the time, it was still quite invisible on the net. I found mostly articles and posts on forums announcing them.